Sub-block based motion candidate selection and signaling

ABSTRACT

Devices, systems and methods for digital video coding, which include sub-block based inter prediction methods, are described. An exemplary method for video processing includes determining, for a conversion between a current block of video and a bitstream representation of the video, a maximum number of candidates in a sub-block based merge candidate list and/or whether to add sub-block based temporal motion vector prediction (SbTMVP) candidates to the sub-block based merge candidate list based on whether temporal motion vector prediction (TMVP) is enabled for use during the conversion or whether a current picture referencing (CPR) coding mode is used for the conversion, and performing, based on the determining, the conversion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international No.PCT/CN2019/120314, filed on Nov. 22, 2019, which claims the priority toand benefits of International Patent Application No. PCT/CN2018/116889,filed on Nov. 22, 2018, International Patent Application No.PCT/CN2018/125420, filed on Dec. 29, 2018, International PatentApplication No. PCT/CN2019/100396, filed on Aug. 13, 2019, andInternational Patent Application No. PCT/CN2019/107159, filed on Sep.22, 2019. The entire disclosures of the aforementioned applications areincorporated by reference as part of the disclosure of this application.

TECHNICAL FIELD

This patent document relates to image and video coding and decoding.

BACKGROUND

In spite of the advances in video compression, digital video stillaccounts for the largest bandwidth use on the internet and other digitalcommunication networks. As the number of connected user devices capableof receiving and displaying video increases, it is expected that thebandwidth demand for digital video usage will continue to grow.

SUMMARY

Devices, systems and methods related to digital video coding, whichinclude sub-block based inter prediction methods, are described. Thedescribed methods may be applied to both the existing video codingstandards (e.g., High Efficiency Video Coding (HEVC) and/or VersatileVideo Coding (VVC)) and future video coding standards or video codecs.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes determining,for a conversion between a current block of video and a bitstreamrepresentation of the video, a maximum number of candidates (ML) in asub-block based merge candidate list and/or whether to add sub-blockbased temporal motion vector prediction (SbTMVP) candidates to thesub-block based merge candidate list based on whether temporal motionvector prediction (TMVP) is enabled for use during the conversion orwhether a current picture referencing (CPR) coding mode is used for theconversion; and performing, based on the determining, the conversion.

In another representative aspect, the disclosed technology may be usedto provide a method for video processing. This method includesdetermining, for a conversion between a current block of video and abitstream representation of the video, a maximum number of candidates(ML) in a sub-block based merge candidate list based on whether atemporal motion vector prediction (TMVP), a sub-block based temporalmotion vector prediction (SbTMVP), and an affine coding mode are enabledfor use during the conversion; and performing, based on the determining,the conversion.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesdetermining, for a conversion between a current block of a first videosegment of a video and a bitstream representation of the video, that asub-block based motion vector prediction (SbTMVP) mode is disabled forthe conversion due to a temporal motion vector prediction (TMVP) modebeing disabled at a first video segment level; and performing theconversion based on the determining, wherein the bitstreamrepresentation complies with a format that specifies whether anindication of the SbTMVP mode is included and/or a position of theindication of the SbTMVP mode in a merge candidate list, with respect toan indication of the TMVP mode.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesperforming a conversion between a current block of a video that is codedusing a sub-block based temporal motion vector prediction (SbTMVP) toolor a temporal motion vector prediction (TMVP) tool and a bitstreamrepresentation of the video, wherein a coordinate of a correspondingposition of the current block or a sub-block of the current block isselectively masked using a mask based on a compression of motion vectorsassociated with the SbTMVP tool or the TMVP tool, and wherein anapplication of the mask comprises computing a bitwise AND operationbetween a value of the coordinate and a value of the mask.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesdetermining, based on one or more characteristics of a current block ofa video segment of a video, a valid corresponding region of the currentblock for an application of a sub-block based motion vector prediction(SbTMVP) tool on the current block; and performing, based on thedetermining, a conversion between the current block and a bitstreamrepresentation of the video.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesdetermining, for a current block of a video that is coded using asub-block based temporal motion vector prediction (SbTMVP) tool, adefault motion vector; and performing, based on the determining, aconversion between the current block and a bitstream representation ofthe video, wherein the default motion vector is determined in case thata motion vector is not obtained from a block covering a correspondingposition in the collocated picture that is associated with a centerposition of the current block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesinferring, for a current block of a video segment of a video, that asub-block based temporal motion vector prediction (SbTMVP) tool or atemporal motion vector prediction (TMVP) tool is disabled for the videosegment in case that a current picture of the current block is areference picture with an index set to M in a reference picture list X,wherein M and X are integers, and wherein X=0 or X=1; and performing,based on the inferring, a conversion between the current block and abitstream representation of the video.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesdetermining, for a current block of a video, that an application of ansub-block based temporal motion vector prediction (SbTMVP) tool isenabled in case that a current picture of the current block is areference picture with an index set to M in a reference picture list X,wherein M and X are integers; and performing, based on the determining,a conversion between the current block and a bitstream representation ofthe video.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesperforming a conversion between a current block of a video and abitstream representation of the video, wherein the current block iscoded using a sub-block based coding tool, and wherein performing theconversion comprises using a plurality of bins (N) to code a sub-blockmerge index with a unified method in case that a sub-block basedtemporal motion vector prediction (SbTMVP) tool is enabled or disabled.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesdetermining, for a current block of a video coded using a subblock-basedtemporal motion vector prediction (SbTMVP) tool, a motion vector used bythe SbTMVP tool to locate a corresponding block in a picture differentfrom a current picture comprising the current block; and performing,based on the determining, a conversion between the current block and abitstream representation of the video.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesdetermining, for a conversion between a current block of a video and abitstream representation of the video, whether a zero motion affinemerge candidate is inserted into a sub-block merge candidate list basedon whether affine prediction is enabled for the conversion of thecurrent block; and performing, based on the determining, the conversion.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesinserting, for a conversion between a current block of a video and abitstream representation of the video that uses a sub-block mergecandidate list, zero motion non-affine padding candidates into thesub-block merge candidate list in case that the sub-block mergecandidate list is not fulfilled; and performing, subsequent to theinserting, the conversion.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This method includesdetermining, for a conversion between a current block of a video and abitstream representation of the video, motion vectors using a rule thatdetermines that the motion vectors are derived from one or more motionvectors of a block covering a corresponding position in a collocatedpicture; and performing, based on the motion vectors, the conversion.

In yet another example aspect, a video encoder apparatus is disclosed.The video encoder apparatus includes a processor that is configured toimplement a method described herein.

In yet another example aspect, a video decoder apparatus is disclosed.The video decoder apparatus includes a processor that is configured toimplement a method described herein.

In yet another aspect, a computer readable medium having code storedthereupon is disclosed. The code, when executed by a processor, causesthe processor to implement a method described in the present document.

These, and other, aspects are described in the present document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of derivation process for merge candidates listconstruction.

FIG. 2 shows example positions of spatial merge candidates.

FIG. 3 shows an example of candidate pairs considered for redundancycheck of spatial merge candidates.

FIGS. 4A and 4B show example positions for a second prediction unit (PU)of N×2N and 2N×N partitions.

FIG. 5 is an example illustration of motion vector scaling for temporalmerge candidate.

FIG. 6 shows example candidate positions for temporal merge candidate,C0 and C1.

FIG. 7 shows an example of combined bi-predictive merge candidate.

FIG. 8 shows an example derivation process for motion vector predictioncandidates.

FIG. 9 is an example illustration of motion vector scaling for spatialmotion vector candidate.

FIG. 10 shows an example of alternative temporal motion vectorprediction (ATMVP) motion prediction for a CU.

FIG. 11 shows an example of one CU with four sub-blocks (A-D) and itsneighbouring blocks (a-d).

FIG. 12 is a flowchart of an example of encoding with different MVprecision

FIGS. 13A and 13B show 135 degree partition type (splitting fromtop-left corner to bottom-right corner) and 45 degree splittingpatterns, respectively.

FIG. 14 shows an example of position of the neighboring blocks.

FIG. 15 shows examples of above and left blocks.

FIGS. 16A and 16B show examples of 2 control point motion vectors(CPMVs) and 3 CPMVs, respectively.

FIG. 17 shows an example of affine motion vector field (MVF) persub-block.

FIGS. 18A and 18B show examples of 4 and 6 parameter affine models,respectively.

FIG. 19 shows an example of MVP for AF_INTER for inherited affinecandidates.

FIG. 20 shows an example of constructing affine motion predictors inAF_INTER.

FIGS. 21A and 21B show examples of control point motion vectors inaffine coding in AF_MERGE.

FIG. 22 shows examples of candidate positions for affine merge mode.

FIG. 23 shows an example of intra-picture block copy operation.

FIG. 24 shows an example of a valid corresponding region in thecollocated picture.

FIG. 25 shows an example flowchart for history based motion vectorprediction.

FIG. 26 shows modified merge list construction process.

FIG. 27 shows an example embodiment of the proposed valid region whenthe current block is inside a basic region.

FIG. 28 shows an example embodiment of a valid region when the currentblock is not inside a basic region.

FIGS. 29A and 29B show existing and proposed examples of locations foridentification of default motion information, respectively.

FIGS. 30-42 are flowcharts for examples of method of video processing.

FIG. 43 is a block diagram of an example of a hardware platform forimplementing a visual media decoding or a visual media encodingtechnique described in the present document.

FIG. 44 is a block diagram of an example video processing system inwhich disclosed techniques may be implemented.

DETAILED DESCRIPTION

The present document provides various techniques that can be used by adecoder of video bitstreams to improve the quality of decompressed ordecoded digital video or images. Furthermore, a video encoder may alsoimplement these techniques during the process of encoding in order toreconstruct decoded frames used for further encoding.

Section headings are used in the present document for ease ofunderstanding and do not limit the embodiments and techniques to thecorresponding sections. As such, embodiments from one section can becombined with embodiments from other sections.

1. Summary

This patent document is related to video coding technologies.Specifically, it is related to motion vector coding in video coding. Itmay be applied to the existing video coding standard like HEVC, or thestandard (Versatile Video Coding) to be finalized. It may be alsoapplicable to future video coding standards or video codec.

2. Introductory Remarks

Video coding standards have evolved primarily through the development ofthe well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 andH.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the twoorganizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, thevideo coding standards are based on the hybrid video coding structurewherein temporal prediction plus transform coding are utilized. Toexplore the future video coding technologies beyond HEVC, Joint VideoExploration Team (JVET) was founded by VCEG and MPEG jointly in 2015.Since then, many new methods have been adopted by JVET and put into thereference software named Joint Exploration Model (JEM). In April 2018,the Joint Video Expert Team (JVET) between VCEG (Q6/16) and ISO/IEC JTC1SC29/WG11 (MPEG) was created to work on the VVC standard targeting at50% bitrate reduction compared to HEVC.

The latest version of VVC draft, i.e., Versatile Video Coding (Draft 3)is found at:

http://phenix.it-sudparis.eu/jvet/doc_end_user/documents/12_Macao/wg11/JVET-L1001-v2.zipThe latest reference software of VVC, named VTM, could be found at:

https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/tags/VTM-3.Orc1

2.1 Inter Prediction in HEVC/H.265

Each inter-predicted PU has motion parameters for one or two referencepicture lists.

Motion parameters include a motion vector and a reference picture index.Usage of one of the two reference picture lists may also be signalledusing inter_pred_idc. Motion vectors may be explicitly coded as deltasrelative to predictors.

When a CU is coded with skip mode, one PU is associated with the CU, andthere are no significant residual coefficients, no coded motion vectordelta or reference picture index. A merge mode is specified whereby themotion parameters for the current PU are obtained from neighbouring PUs,including spatial and temporal candidates. The merge mode can be appliedto any inter-predicted PU, not only for skip mode. The alternative tomerge mode is the explicit transmission of motion parameters, wheremotion vector (to be more precise, motion vector differences (MVD)compared to a motion vector predictor), corresponding reference pictureindex for each reference picture list and reference picture list usageare signalled explicitly per each PU. Such a mode is named advancedmotion vector prediction (AMVP) in this disclosure.

When signalling indicates that one of the two reference picture lists isto be used, the PU is produced from one block of samples. This isreferred to as ‘uni-prediction’. Uni-prediction is available both forP-slices and B-slices.

When signalling indicates that both of the reference picture lists areto be used, the PU is produced from two blocks of samples. This isreferred to as ‘bi-prediction’. Bi-prediction is available for B-slicesonly.

The following text provides the details on the inter prediction modesspecified in HEVC. The description will start with the merge mode.

2.1.1 Reference Picture List

In HEVC, the term inter prediction is used to denote prediction derivedfrom data elements (e.g., sample values or motion vectors) of referencepictures other than the current decoded picture. Like in H.264/AVC, apicture can be predicted from multiple reference pictures. The referencepictures that are used for inter prediction are organized in one or morereference picture lists. The reference index identifies which of thereference pictures in the list should be used for creating theprediction signal.

A single reference picture list, List 0, is used for a P slice and tworeference picture lists, List 0 and List 1 are used for B slices. Itshould be noted reference pictures included in List 0/1 could be frompast and future pictures in terms of capturing/display order.

2.1.2 Merge Mode 2.1.2.1 Derivation of Candidates for Merge Mode

When a PU is predicted using merge mode, an index pointing to an entryin the merge candidates list is parsed from the bitstream and used toretrieve the motion information. The construction of this list isspecified in the HEVC standard and can be summarized according to thefollowing sequence of steps:

-   -   Step 1: Initial candidates derivation        -   Step 1.1: Spatial candidates derivation        -   Step 1.2: Redundancy check for spatial candidates        -   Step 1.3: Temporal candidates derivation    -   Step 2: Additional candidates insertion        -   Step 2.1: Creation of bi-predictive candidates        -   Step 2.2: Insertion of zero motion candidates

These steps are also schematically depicted in FIG. 1. For spatial mergecandidate derivation, a maximum of four merge candidates are selectedamong candidates that are located in five different positions. Fortemporal merge candidate derivation, a maximum of one merge candidate isselected among two candidates. Since constant number of candidates foreach PU is assumed at decoder, additional candidates are generated whenthe number of candidates obtained from step 1 does not reach the maximumnumber of merge candidate (MaxNumMergeCand) which is signalled in sliceheader. Since the number of candidates is constant, index of best mergecandidate is encoded using truncated unary binarization (TU). If thesize of CU is equal to 8, all the PUs of the current CU share a singlemerge candidate list, which is identical to the merge candidate list ofthe 2N×2N prediction unit.

In the following, the operations associated with the aforementionedsteps are detailed. 2.1.2.2 Spatial candidates derivation

In the derivation of spatial merge candidates, a maximum of four mergecandidates are selected among candidates located in the positionsdepicted in FIG. 2. The order of derivation is A₁, B₁, B₀, A₀ and B₂.Position B₂ is considered only when any PU of position A₁, B₁, B₀, A₀ isnot available (e.g. because it belongs to another slice or tile) or isintra coded. After candidate at position A₁ is added, the addition ofthe remaining candidates is subject to a redundancy check which ensuresthat candidates with same motion information are excluded from the listso that coding efficiency is improved. To reduce computationalcomplexity, not all possible candidate pairs are considered in thementioned redundancy check. Instead only the pairs linked with an arrowin FIG. 3 are considered and a candidate is only added to the list ifthe corresponding candidate used for redundancy check has not the samemotion information. Another source of duplicate motion information isthe “second PU” associated with partitions different from 2N×2N. As anexample, FIGS. 4A-4B depicts the second PU for the case of N×2N and2N×N, respectively. When the current PU is partitioned as N×2N,candidate at position A₁ is not considered for list construction. Infact, by adding this candidate will lead to two prediction units havingthe same motion information, which is redundant to just have one PU in acoding unit. Similarly, position B₁ is not considered when the currentPU is partitioned as 2N×N. 2.1.2.3 Temporal candidates derivation

In this step, only one candidate is added to the list. Particularly, inthe derivation of this temporal merge candidate, a scaled motion vectoris derived based on co-located PU belonging to the picture which has thesmallest POC difference with current picture within the given referencepicture list. The reference picture list to be used for derivation ofthe co-located PU is explicitly signalled in the slice header. Thescaled motion vector for temporal merge candidate is obtained asillustrated by the dotted line in FIG. 5, which is scaled from themotion vector of the co-located PU using the POC distances, tb and td,where tb is defined to be the POC difference between the referencepicture of the current picture and the current picture and td is definedto be the POC difference between the reference picture of the co-locatedpicture and the co-located picture. The reference picture index oftemporal merge candidate is set equal to zero. A practical realizationof the scaling process is described in the HEVC specification. For aB-slice, two motion vectors, one is for reference picture list 0 and theother is for reference picture list 1, are obtained and combined to makethe bi-predictive merge candidate.

FIG. 5 is an illustration of motion vector scaling for temporal mergecandidate.

In the co-located PU (Y) belonging to the reference frame, the positionfor the temporal candidate is selected between candidates C₀ and C₁, asdepicted in FIG. 6. If PU at position C₀ is not available, is intracoded, or is outside of the current coding tree unit (CTU aka. LCU,largest coding unit) row, position C₁ is used. Otherwise, position C₀ isused in the derivation of the temporal merge candidate.

FIG. 6 shows examples of candidate positions for temporal mergecandidate, C0 and C1.

2.1.2.4 Additional Candidates Insertion

Besides spatial and temporal merge candidates, there are two additionaltypes of merge candidates: combined bi-predictive merge candidate andzero merge candidate. Combined bi-predictive merge candidates aregenerated by utilizing spatial and temporal merge candidates. Combinedbi-predictive merge candidate is used for B-Slice only. The combinedbi-predictive candidates are generated by combining the first referencepicture list motion parameters of an initial candidate with the secondreference picture list motion parameters of another. If these two tuplesprovide different motion hypotheses, they will form a new bi-predictivecandidate. As an example, FIG. 7 depicts the case when two candidates inthe original list (on the left), which have mvL0 and refIdxL0 or mvL1and refIdxL1, are used to create a combined bi-predictive mergecandidate added to the final list (on the right). There are numerousrules regarding the combinations which are considered to generate theseadditional merge candidates.

Zero motion candidates are inserted to fill the remaining entries in themerge candidates list and therefore hit the MaxNumMergeCand capacity.These candidates have zero spatial displacement and a reference pictureindex which starts from zero and increases every time a new zero motioncandidate is added to the list.

More specifically, the following steps are performed in order till themerge list is full:

-   -   1. Set variable numRef to either number of reference picture        associated with list 0 for P slice, or the minimum number of        reference pictures in two lists for B slice;    -   2. Add non-repeated zero motion candidates:        -   For variable i being 0 . . . numRef−1, add a default motion            candidate with MV set to (0, 0) and reference picture index            set to i for list 0 (if P slice), or for both lists (if B            slice).    -   3. Add repeated zero motion candidates with MV set to (0, 0),        reference picture index of list 0 set to 0 (if P slice) and        reference picture indices of both lists set to 0 (if B slice).

Finally, no redundancy check is performed on these candidates.

2.1.3 Advanced Motion Vector Prediction (AMVP)

AMVP exploits spatio-temporal correlation of motion vector withneighbouring PUs, which is used for explicit transmission of motionparameters. For each reference picture list, a motion vector candidatelist is constructed by firstly checking availability of left, abovetemporally neighbouring PU positions, removing redundant candidates andadding zero vector to make the candidate list to be constant length.Then, the encoder can select the best predictor from the candidate listand transmit the corresponding index indicating the chosen candidate.Similarly with merge index signalling, the index of the best motionvector candidate is encoded using truncated unary. The maximum value tobe encoded in this case is 2 (see FIG. 8). In the following sections,details about derivation process of motion vector prediction candidateare provided.

2.1.3.1 Derivation of AMVP Candidates

FIG. 8 summarizes derivation process for motion vector predictioncandidate.

In motion vector prediction, two types of motion vector candidates areconsidered: spatial motion vector candidate and temporal motion vectorcandidate. For spatial motion vector candidate derivation, two motionvector candidates are eventually derived based on motion vectors of eachPU located in five different positions as depicted in FIG. 2.

For temporal motion vector candidate derivation, one motion vectorcandidate is selected from two candidates, which are derived based ontwo different co-located positions. After the first list ofspatio-temporal candidates is made, duplicated motion vector candidatesin the list are removed. If the number of potential candidates is largerthan two, motion vector candidates whose reference picture index withinthe associated reference picture list is larger than 1 are removed fromthe list. If the number of spatio-temporal motion vector candidates issmaller than two, additional zero motion vector candidates is added tothe list.

2.1.3.2 Spatial Motion Vector Candidates

In the derivation of spatial motion vector candidates, a maximum of twocandidates are considered among five potential candidates, which arederived from PUs located in positions as depicted in FIG. 2, thosepositions being the same as those of motion merge. The order ofderivation for the left side of the current PU is defined as A₀, A₁, andscaled A₀, scaled A₁. The order of derivation for the above side of thecurrent PU is defined as B₀, B₁, B₂, scaled B₀, scaled B₁, scaled B₂.For each side there are therefore four cases that can be used as motionvector candidate, with two cases not required to use spatial scaling,and two cases where spatial scaling is used. The four different casesare summarized as follows.

-   -   No spatial scaling        -   (1) Same reference picture list, and same reference picture            index (same POC)        -   (2) Different reference picture list, but same reference            picture (same POC)    -   Spatial scaling        -   (3) Same reference picture list, but different reference            picture (different POC)        -   (4) Different reference picture list, and different            reference picture (different POC)

The no-spatial-scaling cases are checked first followed by the spatialscaling. Spatial scaling is considered when the POC is different betweenthe reference picture of the neighbouring PU and that of the current PUregardless of reference picture list. If all PUs of left candidates arenot available or are intra coded, scaling for the above motion vector isallowed to help parallel derivation of left and above MV candidates.Otherwise, spatial scaling is not allowed for the above motion vector.

In a spatial scaling process, the motion vector of the neighbouring PUis scaled in a similar manner as for temporal scaling, as depicted asFIG. 9. The main difference is that the reference picture list and indexof current PU is given as input; the actual scaling process is the sameas that of temporal scaling.

2.1.3.3 Temporal Motion Vector Candidates

Apart for the reference picture index derivation, all processes for thederivation of temporal merge candidates are the same as for thederivation of spatial motion vector candidates (see FIG. 6). Thereference picture index is signalled to the decoder.

2.2 Sub-CU Based Motion Vector Prediction Methods in JEM

In the JEM with QTBT, each CU can have at most one set of motionparameters for each prediction direction. Two sub-CU level motion vectorprediction methods are considered in the encoder by splitting a large CUinto sub-CUs and deriving motion information for all the sub-CUs of thelarge CU. Alternative temporal motion vector prediction (ATMVP) methodallows each CU to fetch multiple sets of motion information frommultiple blocks smaller than the current CU in the collocated referencepicture. In spatial-temporal motion vector prediction (STMVP) methodmotion vectors of the sub-CUs are derived recursively by using thetemporal motion vector predictor and spatial neighbouring motion vector.

To preserve more accurate motion field for sub-CU motion prediction, themotion compression for the reference frames is currently disabled.

FIG. 10 shows an example of ATMVP motion prediction for a CU.

2.2.1 Alternative Temporal Motion Vector Prediction

In the alternative temporal motion vector prediction (ATMVP) method, themotion vectors temporal motion vector prediction (TMVP) is modified byfetching multiple sets of motion information (including motion vectorsand reference indices) from blocks smaller than the current CU. In someimplementations, the sub-CUs are square N×N blocks (N is set to 4 bydefault).

ATMVP predicts the motion vectors of the sub-CUs within a CU in twosteps. The first step is to identify the corresponding block in areference picture with a so-called temporal vector. The referencepicture is called the motion source picture. The second step is to splitthe current CU into sub-CUs and obtain the motion vectors as well as thereference indices of each sub-CU from the block corresponding to eachsub-CU.

In the first step, a reference picture and the corresponding block isdetermined by the motion information of the spatial neighbouring blocksof the current CU. To avoid the repetitive scanning process ofneighbouring blocks, the first merge candidate in the merge candidatelist of the current CU is used. The first available motion vector aswell as its associated reference index are set to be the temporal vectorand the index to the motion source picture. This way, in ATMVP, thecorresponding block may be more accurately identified, compared withTMVP, wherein the corresponding block (sometimes called collocatedblock) is always in a bottom-right or center position relative to thecurrent CU.

In the second step, a corresponding block of the sub-CU is identified bythe temporal vector in the motion source picture, by adding to thecoordinate of the current CU the temporal vector. For each sub-CU, themotion information of its corresponding block (the smallest motion gridthat covers the center sample) is used to derive the motion informationfor the sub-CU. After the motion information of a corresponding N×Nblock is identified, it is converted to the motion vectors and referenceindices of the current sub-CU, in the same way as TMVP of HEVC, whereinmotion scaling and other procedures apply. For example, the decoderchecks whether the low-delay condition (i.e. the POCs of all referencepictures of the current picture are smaller than the POC of the currentpicture) is fulfilled and possibly uses motion vector MV_(x) (the motionvector corresponding to reference picture list X) to predict motionvector MV_(y) (with X being equal to 0 or 1 and Y being equal to 1-X)for each sub-CU.

2.2.2 Spatial-Temporal Motion Vector Prediction (STMVP)

In this method, the motion vectors of the sub-CUs are derivedrecursively, following raster scan order. FIG. 11 illustrates thisconcept. Let us consider an 8×8 CU which contains four 4×4 sub-CUs A, B,C, and D. The neighbouring 4×4 blocks in the current frame are labelledas a, b, c, and d.

The motion derivation for sub-CU A starts by identifying its two spatialneighbours. The first neighbour is the N×N block above sub-CU A (blockc). If this block c is not available or is intra coded the other N×Nblocks above sub-CU A are checked (from left to right, starting at blockc). The second neighbour is a block to the left of the sub-CU A (blockb). If block b is not available or is intra coded other blocks to theleft of sub-CU A are checked (from top to bottom, staring at block b).The motion information obtained from the neighbouring blocks for eachlist is scaled to the first reference frame for a given list. Next,temporal motion vector predictor (TMVP) of sub-block A is derived byfollowing the same procedure of TMVP derivation as specified in HEVC.The motion information of the collocated block at location D is fetchedand scaled accordingly. Finally, after retrieving and scaling the motioninformation, all available motion vectors (up to 3) are averagedseparately for each reference list. The averaged motion vector isassigned as the motion vector of the current sub-CU.

2.2.3 Sub-CU Motion Prediction Mode Signalling

The sub-CU modes are enabled as additional merge candidates and there isno additional syntax element required to signal the modes. Twoadditional merge candidates are added to merge candidates list of eachCU to represent the ATMVP mode and STMVP mode. Up to seven mergecandidates are used, if the sequence parameter set indicates that ATMVPand STMVP are enabled. The encoding logic of the additional mergecandidates is the same as for the merge candidates in the HM, whichmeans, for each CU in P or B slice, two more RD checks is needed for thetwo additional merge candidates.

In the JEM, all bins of merge index is context coded by CABAC. While inHEVC, only the first bin is context coded and the remaining bins arecontext by-pass coded.

2.3 Inter Prediction Methods in VVC

There are several new coding tools for inter prediction improvement,such as Adaptive motion vector difference resolution (AMVR) forsignaling MVD, affine prediction mode, Triangular prediction mode (TPM),ATMVP, Generalized Bi-Prediction (GBI), Bi-directional Optical flow(BIO).

2.3.1 Adaptive Motion Vector Difference Resolution

In HEVC, motion vector differences (MVDs) (between the motion vector andpredicted motion vector of a PU) are signalled in units of quarter lumasamples when use_integer_mv_flag is equal to 0 in the slice header. Inthe VVC, a locally adaptive motion vector resolution (LAMVR) isintroduced. In the VVC, MVD can be coded in units of quarter lumasamples, integer luma samples or four luma samples (i.e., ¼-pel, 1-pel,4-pel). The MVD resolution is controlled at the coding unit (CU) level,and MVD resolution flags are conditionally signalled for each CU thathas at least one non-zero MVD components.

For a CU that has at least one non-zero MVD components, a first flag issignalled to indicate whether quarter luma sample MV precision is usedin the CU. When the first flag (equal to 1) indicates that quarter lumasample MV precision is not used, another flag is signalled to indicatewhether integer luma sample MV precision or four luma sample MVprecision is used.

When the first MVD resolution flag of a CU is zero, or not coded for aCU (meaning all MVDs in the CU are zero), the quarter luma sample MVresolution is used for the CU. When a CU uses integer-luma sample MVprecision or four-luma-sample MV precision, the MVPs in the AMVPcandidate list for the CU are rounded to the corresponding precision.

In the encoder, CU-level RD checks are used to determine which MVDresolution is to be used for a CU. That is, the CU-level RD check isperformed three times for each MVD resolution. To accelerate encoderspeed, the following encoding schemes are applied in the JEM.

-   -   During RD check of a CU with normal quarter luma sample MVD        resolution, the motion information of the current CU (integer        luma sample accuracy) is stored. The stored motion information        (after rounding) is used as the starting point for further small        range motion vector refinement during the RD check for the same        CU with integer luma sample and 4 luma sample MVD resolution so        that the time-consuming motion estimation process is not        duplicated three times.    -   RD check of a CU with 4 luma sample MVD resolution is        conditionally invoked. For a CU, when RD cost integer luma        sample MVD resolution is much larger than that of quarter luma        sample MVD resolution, the RD check of 4 luma sample MVD        resolution for the CU is skipped.

The encoding process is shown in FIG. 12. First, ¼ pel MV is tested andthe RD cost is calculated and denoted as RDCost0, then integer MV istested and the RD cost is denoted as RDCost1. If RDCost1<th*RDCost0(wherein th is a positive value), then 4-pel MV is tested; otherwise,4-pel MV is skipped. Basically, motion information and RD cost etc. arealready known for ¼ pel MV when checking integer or 4-pel MV, which canbe reused to speed up the encoding process of integer or 4-pel MV.

2.3.2 Triangular Prediction Mode

The concept of the triangular prediction mode (TPM) is to introduce anew triangular partition for motion compensated prediction. As shown inFIGS. 13A-13B, it splits a CU into two triangular prediction units, ineither diagonal or inverse diagonal direction. Each triangularprediction unit in the CU is inter-predicted using its ownuni-prediction motion vector and reference frame index which are derivedfrom a single uni-prediction candidate list. An adaptive weightingprocess is performed to the diagonal edge after predicting thetriangular prediction units. Then, the transform and quantizationprocess are applied to the whole CU. It is noted that this mode is onlyapplied to merge mode (note: skip mode is treated as a special mergemode).

FIG. 13A-13B are an illustration of splitting a CU into two triangularprediction units (two splitting patterns): FIG. 13A: 135 degreepartition type (splitting from top-left corner to bottom-right corner);FIG. 13B: 45 degree splitting patterns.

2.3.2.1 Uni-Prediction Candidate List for TPM

The uni-prediction candidate list, named TPM motion candidate list,consists of five uni-prediction motion vector candidates. It is derivedfrom seven neighboring blocks including five spatial neighboring blocks(1 to 5) and two temporal co-located blocks (6 to 7), as shown in FIG.14. The motion vectors of the seven neighboring blocks are collected andput into the uni-prediction candidate list according in the order ofuni-prediction motion vectors, L0 motion vector of bi-prediction motionvectors, L1 motion vector of bi-prediction motion vectors, and averagedmotion vector of the L0 and L1 motion vectors of bi-prediction motionvectors. If the number of candidates is less than five, zero motionvector is added to the list. Motion candidates added in this list forTPM are called TPM candidates, motion information derived fromspatial/temporal blocks are called regular motion candidates.

More specifically, the following steps are involved:

-   -   1) Obtain regular motion candidates from A₁, B₁, B₀, A₀, B₂, Col        and Col2 (corresponding to block 1-7 in FIG. 14) with full        pruning operations when adding a regular motion candidate from        spatial neighboring blocks.    -   2) Set variable numCurrMergeCand=0    -   3) For each regular motion candidates derived from A₁, B₁, B₀,        A₀, B₂, Col and Col2, if not pruned and numCurrMergeCand is less        than 5, if the regular motion candidate is uni-prediction        (either from List 0 or List 1), it is directly added to the        merge list as an TPM candidate with numCurrMergeCand increased        by 1. Such a TPM candidate is named ‘originally uni-predicted        candidate’.        -   Full pruning is applied.    -   4) For each motion candidates derived from A₁, B₁, B₀, A₀, B₂,        Col and Col2, if not pruned, and numCurrMergeCand is less than        5, if the regular motion candidate is bi-prediction, the motion        information from List 0 is added to the TPM merge list (that is,        modified to be uni-prediction from List 0) as a new TPM        candidate and numCurrMergeCand increased by 1. Such a TPM        candidate is named ‘Truncated List0-predicted candidate’.        -   Full pruning is applied.    -   5) For each motion candidates derived from A₁, B₁, B₀, A₀, B₂,        Col and Col2, if not pruned, and numCurrMergeCand is less than        5, if the regular motion candidate is bi-prediction, the motion        information from List 1 is added to the TPM merge list (that is,        modified to be uni-prediction from List 1) and numCurrMergeCand        increased by 1. Such a TPM candidate is named ‘Truncated        List1-predicted candidate’.        -   Full pruning is applied.    -   6) For each motion candidates derived from A₁, B₁, B₀, A₀, B₂,        Col and Col2, if not pruned, and numCurrMergeCand is less than        5, if the regular motion candidate is bi-prediction,        -   If List 0 reference picture's slice QP is smaller than List            1 reference picture's slice QP, the motion information of            List 1 is firstly scaled to List 0 reference picture, and            the average of the two MVs (one is from original List 0, and            the other is the scaled MV from List 1) is added to the TPM            merge list, such a candidate is called averaged            uni-prediction from List 0 motion candidate and            numCurrMergeCand increased by 1.        -   Otherwise, the motion information of List 0 is firstly            scaled to List 1 reference picture, and the average of the            two MVs (one is from original List 1, and the other is the            scaled MV from List 0) is added to the TPM merge list, such            a TPM candidate is called averaged uni-prediction from List            1 motion candidate and numCurrMergeCand increased by 1.        -   Full pruning is applied.    -   7) If numCurrMergeCand is less than 5, zero motion vector        candidates are added.

When inserting a candidate to the list, if it has to be compared to allpreviously added candidates to see whether it is identical to one ofthem, such a process is called full pruning.

2.3.2.2 Adaptive Weighting Process

After predicting each triangular prediction unit, an adaptive weightingprocess is applied to the diagonal edge between the two triangularprediction units to derive the final prediction for the whole CU. Twoweighting factor groups are defined as follows:

-   -   1^(st) weighting factor group: {7/8, 6/8, 4/8, 2/8, 1/8} and        {7/8, 4/8, 1/8} are used for the luminance and the chrominance        samples, respectively;    -   2^(nd) weighting factor group: {7/8, 6/8, 5/8, 4/8, 3/8, 2/8,        1/8} and {6/8, 4/8, 2/8} are used for the luminance and the        chrominance samples, respectively.

Weighting factor group is selected based on the comparison of the motionvectors of two triangular prediction units. The 2^(nd) weighting factorgroup is used when the reference pictures of the two triangularprediction units are different from each other or their motion vectordifference is larger than 16 pixels. Otherwise, the 1^(st) weightingfactor group is used.

2.3.2.3 Signaling of Triangular Prediction Mode (TPM)

One bit flag to indicate whether TPM is used may be firstly signaled.Afterwards, the indications of two splitting patterns (as depicted inFIGS. 13A-13B), and selected merge indices for each of the twopartitions are further signaled.

2.3.2.3.1 Signaling of TPM Flag

Let's denote one luma block's width and height by W and H, respectively.If W*H<64, triangular prediction mode is disabled.

When one block is coded with affine mode, triangular prediction mode isalso disabled.

When one block is coded with merge mode, one bit flag may be signaled toindicate whether the triangular prediction mode is enabled or disabledfor the block.

The flag is coded with 3 contexts, based on the following equation:

Ctxindex=((left block Lavailable && L is coded with TPM?)1:0)+((Aboveblock Aavailable && A is coded with TPM?)1:0);

FIG. 15 shows examples of neighboring blocks (A and L) used for contextselection in TPM flag coding.

2.3.2.3.2 Signaling of an Indication of Two Splitting Patterns (asDepicted in FIG. 13), and Selected Merge Indices for Each of the TwoPartitions

It is noted that splitting patterns, merge indices of two partitions arejointly coded. In an existing implementation, it is restricted that thetwo partitions couldn't use the same reference index. Therefore, thereare 2 (splitting patterns)*N (maximum number of merge candidates)*(N−1)possibilities wherein N is set to 5. One indication is coded and themapping between the splitting patterns, two merge indices and codedindication are derived from the array defined below:

const  uint8_t  g_TriangleCombination[TRIANGLE_MAX_NUM_CANDS][3] = {  {0, 1, 0}, {1, 0, 1}, {1, 0, 2}, {0, 0, 1}, {0, 2, 0},  {1, 0, 3}, {1, 0, 4}, {1, 1, 0}, {0, 3, 0}, {0, 4, 0},  {0, 0, 2}, {0, 1, 2}, {1, 1, 2}, {0, 0, 4}, {0, 0, 3},  {0, 1, 3}, {0, 1, 4}, {1, 1, 4}, {1, 1, 3}, {1, 2, 1},  {1, 2, 0}, {0, 2, 1}, {0, 4, 3}, {1, 3, 0}, {1, 3, 2},  {1, 3, 4}, {1, 4, 0}, {1, 3, 1}, {1, 2, 3}, {1, 4, 1},  {0, 4, 1}, {0, 2, 3}, {1, 4, 2}, {0, 3, 2}, {1, 4, 3},  {0, 3, 1}, {0, 2, 4}, {1, 2, 4}, {0, 4, 2}, {0, 3, 4}};

splitting patterns (45 degree or 135degree)=g_TriangleCombination[signaled indication][0];

Merge index of candidate A=g_TriangleCombination[signaledindication][1];

Merge index of candidate B=g_TriangleCombination[signaledindication][2];

Once the two motion candidates A and B are derived, the two partitions'(PU1 and PU2) motion information could be set either from A or B.Whether PU1 uses the motion information of merge candidate A or B isdependent on the prediction directions of the two motion candidates.Table 1 shows the relationship between two derived motion candidates Aand B, with the two partitions.

TABLE 1 Derivation of partitions' motion information from derived twomerge candidates (A, B) Prediction Prediction PU1's motion PU2's motiondirection of A direction of B information information L0 L0 A (L0) B(L0) L1 L1 B (L1) A (L1) L0 L1 A (L0) B (L1) L1 L0 B (L0) A (L1)

2.3.2.3.3 Entropy Coding of the Indication (Denoted byMerge_Triangle_Idx)

merge triangle idx is within the range [0, 39], inclusively. K-th orderExponential Golomb (EG) code is used for binarization ofmerge_triangle_idx wherein K is set to 1.

K-Th Order EG

To encode larger numbers in fewer bits (at the expense of using morebits to encode smaller numbers), this can be generalized using anonnegative integer parameter k. To encode a nonnegative integer x in anorder-k exp-Golomb code:

-   -   1. Encode └x/2^(k)┘ using order-0 exp-Golomb code described        above, then    -   2. Encode x mod 2^(k) in binary

TABLE 1 Exp-Golomb-k coding examples x k = 0 k = 1 k = 2 0 1 10 100 1010 11 101 2 011 0100 110 3 00100 0101 111 4 00101 0110 01000 5 001100111 01001 6 00111 001000 01010 7 0001000 001001 01011 8 0001001 00101001100 9 0001010 001011 01101 10 0001011 001100 01110 11 0001100 00110101111 12 0001101 001110 001000 13 0001110 001111 010001 14 000111100010000 0010010 15 000010000 00010001 0010011 16 000010001 000100100010100 17 000010010 00010011 0010101 18 000010011 00010100 0010110 19000010100 00010101 0010111

2.3.3 Affine Motion Compensation Prediction

In HEVC, only translation motion model is applied for motioncompensation prediction (MCP). While in the real world, there are manykinds of motion, e.g. zoom in/out, rotation, perspective motions and theother irregular motions. In VVC, a simplified affine transform motioncompensation prediction is applied with 4-parameter affine model and6-parameter affine model. As shown FIGS. 16A-16B, the affine motionfield of the block is described by two control point motion vectors(CPMVs) for the 4-parameter affine model (FIG. 16A) and 3 CPMVs for the6-parameter affine model (FIG. 16B).

The motion vector field (MVF) of a block is described by the followingequations with the 4-parameter affine model (wherein the 4-parameter aredefined as the variables a, b, e and f) in equation (1) and 6-parameteraffine model (wherein the 4-parameter are defined as the variables a, b,c, d, e and f) in equation (2) respectively:

$\begin{matrix}\left\{ \begin{matrix}{{{mv}^{h}\left( {x,y} \right)} = {{{ax} - {by} + e} = {{\frac{\left( {{mv}_{1}^{h} - {mv}_{0}^{h}} \right)}{w}x} - {\frac{\left( {{mv}_{1}^{v} - {mv}_{0}^{v}} \right)}{w}y} + {mv}_{0}^{h}}}} \\{{{mv}^{v}\left( {x,y} \right)} = {{{bx} + {ay} + f} = {{\frac{\left( {{mv}_{1}^{v} - {mv}_{0}^{v}} \right)}{w}x} + {\frac{\left( {{mv}_{1}^{h} - {mv}_{0}^{h}} \right)}{w}y} + {mv}_{0}^{v}}}}\end{matrix} \right. & (1) \\\left\{ \begin{matrix}{{{mv}^{h}\left( {x,y} \right)} = {{{ax} + {cy} + e} = {{\frac{\left( {{mv}_{1}^{h} - {mv}_{0}^{h}} \right)}{w}x} + {\frac{\left( {{mv}_{1}^{v} - {mv}_{0}^{v}} \right)}{h}y} + {mv}_{0}^{h}}}} \\{{{mv}^{v}\left( {x,y} \right)} = {{{bx} + {dy} + f} = {{\frac{\left( {{mv}_{1}^{v} - {mv}_{0}^{v}} \right)}{w}x} + {\frac{\left( {{mv}_{2}^{v} - {mv}_{0}^{v}} \right)}{h}y} + {mv}_{0}^{v}}}}\end{matrix} \right. & (2)\end{matrix}$

where (mv^(h) ₀, mv^(h) ₀) is motion vector of the top-left cornercontrol point, and (mv^(h) ₁, mv^(h) ₁) is motion vector of thetop-right corner control point and (mv^(h) ₂, mv^(h) ₂) is motion vectorof the bottom-left corner control point, all of the three motion vectorsare called control point motion vectors (CPMV), (x, y) represents thecoordinate of a representative point relative to the top-left samplewithin current block and (mv^(h)(x,y), mv^(v)(x,y)) is the motion vectorderived for a sample located at (x, y). The CP motion vectors may besignaled (like in the affine AMVP mode) or derived on-the-fly (like inthe affine merge mode). w and h are the width and height of the currentblock. In practice, the division is implemented by right-shift with arounding operation. In VTM, the representative point is defined to bethe center position of a sub-block, e.g., when the coordinate of theleft-top corner of a sub-block relative to the top-left sample withincurrent block is (xs, ys), the coordinate of the representative point isdefined to be (xs+2, ys+2). For each sub-block (i.e., 4×4 in VTM), therepresentative point is utilized to derive the motion vector for thewhole sub-block.

In order to further simplify the motion compensation prediction,sub-block based affine transform prediction is applied. To derive motionvector of each M×N (both M and N are set to 4 in current VVC) sub-block,the motion vector of the center sample of each sub-block, as shown inFIG. 17, is calculated according to Equation (1) and (2), and rounded to1/16 fraction accuracy. Then the motion compensation interpolationfilters for 1/16-pel are applied to generate the prediction of eachsub-block with derived motion vector. The interpolation filters for1/16-pel are introduced by the affine mode.

After MCP, the high accuracy motion vector of each sub-block is roundedand saved as the same accuracy as the normal motion vector.

2.3.3.1 Signaling of Affine Prediction

Similar to the translational motion model, there are also two modes forsignaling the side information due affine prediction. They areAFFINE_INTER and AFFINE_MERGE modes.

2.3.3.2 AF_INTER Mode

For CUs with both width and height larger than 8, AF_INTER mode can beapplied. An affine flag in CU level is signalled in the bitstream toindicate whether AF_INTER mode is used.

In this mode, for each reference picture list (List 0 or List 1), anaffine AMVP candidate list is constructed with three types of affinemotion predictors in the following order, wherein each candidateincludes the estimated CPMVs of the current block. The differences ofthe best CPMVs found at the encoder side (such as mv₀ mv₁ mv₂ in FIG.20) and the estimated CPMVs are signalled. In addition, the index ofaffine AMVP candidate from which the estimated CPMVs are derived isfurther signalled.

1) Inherited Affine Motion Predictors

The checking order is similar to that of spatial MVPs in HEVC AMVP listconstruction. First, a left inherited affine motion predictor is derivedfrom the first block in {A1, A0} that is affine coded and has the samereference picture as in current block. Second, an above inherited affinemotion predictor is derived from the first block in {B1, B0, B2} that isaffine coded and has the same reference picture as in current block. Thefive blocks A1, A0, B1, B0, B2 are depicted in FIG. 19.

Once a neighboring block is found to be coded with affine mode, theCPMVs of the coding unit covering the neighboring block are used toderive predictors of CPMVs of current block. For example, if A1 is codedwith non-affine mode and A0 is coded with 4-parameter affine mode, theleft inherited affine MV predictor will be derived from A0. In thiscase, the CPMVs of a CU covering A0, as denoted by MV₀ ^(N) for thetop-left CPMV and MV₁ ^(N) for the top-right CPMV in FIG. 21B areutilized to derive the estimated CPMVs of current block, denoted by MV₀^(C), MV₀ ^(C), MV₂ ^(C) for the top-left (with coordinate (x0, y0)),top-right (with coordinate (x1, y1)) and bottom-right positions (withcoordinate (x2, y2)) of current block.

2) Constructed Affine Motion Predictors

A constructed affine motion predictor consists of control-point motionvectors (CPMVs) that are derived from neighboring inter coded blocks, asshown in FIG. 20, that have the same reference picture. If the currentaffine motion model is 4-parameter affine, the number of CPMVs is 2,otherwise if the current affine motion model is 6-parameter affine, thenumber of CPMVs is 3. The top-left CPMV mv ₀ is derived by the MV at thefirst block in the group {A, B, C} that is inter coded and has the samereference picture as in current block. The top-right CPMV mv ₁ isderived by the MV at the first block in the group {D, E} that is intercoded and has the same reference picture as in current block. Thebottom-left CPMV mv ₂ is derived by the MV at the first block in thegroup {F, G} that is inter coded and has the same reference picture asin current block.

-   -   If the current affine motion model is 4-parameter affine, then a        constructed affine motion predictor is inserted into the        candidate list only if both mv ₀ and mv ₁ mare founded, that is,        mv ₀ and mv ₁ are used as the estimated CPMVs for top-left (with        coordinate (x0, y0)), top-right (with coordinate (x1, y1))        positions of current block.    -   If the current affine motion model is 6-parameter affine, then a        constructed affine motion predictor is inserted into the        candidate list only if mv ₀, mv ₁ and mv ₂ are all founded, that        is, mv ₀, mv ₁ and mv ₂ are used as the estimated CPMVs for        top-left (with coordinate (x0, y0)), top-right (with coordinate        (x1, y1)) and bottom-right (with coordinate (x2, y2)) positions        of current block.

No pruning process is applied when inserting a constructed affine motionpredictor into the candidate list.

3) Normal AMVP Motion Predictors

The following applies until the number of affine motion predictorsreaches the maximum.

-   -   1) Derive an affine motion predictor by setting all CPMVs equal        to mv ₂ if available.    -   2) Derive an affine motion predictor by setting all CPMVs equal        to mv ₁ if available.    -   3) Derive an affine motion predictor by setting all CPMVs equal        to mv ₀ if available.    -   4) Derive an affine motion predictor by setting all CPMVs equal        to HEVC TMVP if available.    -   5) Derive an affine motion predictor by setting all CPMVs to        zero MV.

Note that mv _(i) is already derived in constructed affine motionpredictor.

FIG. 18A shows an example of a 4-parameter affine model. FIG. 18B showsan example of a 6-parameter affine model.

FIG. 19 shows an example of MVP for AF_INTER for inherited affinecandidates.

FIG. 20 shows an example of MVP for AF_INTER for constructed affinecandidates.

In AF_INTER mode, when 4/6-parameter affine mode is used, 2/3 controlpoints are required, and therefore 2/3 MVD needs to be coded for thesecontrol points, as shown in FIG. 18. In an existing implementation, itis proposed to derive the MV as follows, i.e., mvd₁ and mvd₂ arepredicted from mvd₀.

mv ₀ =mv ₀ +mvd ₀

mv ₁ =mv ₁ +mvd ₁ +mvd ₀

mv ₂ =mv ₂ +mvd ₂ +mvd ₀

Wherein mv _(i), mvd_(i) and mv₁ are the predicted motion vector, motionvector difference and motion vector of the top-left pixel (i=0),top-right pixel (i=1) or left-bottom pixel (i=2) respectively, as shownin FIG. 18B. Please note that the addition of two motion vectors (e.g.,mvA(xA, yA) and mvB(xB, yB)) is equal to summation of two componentsseparately, that is, newMV=mvA+mvB and the two components of newMV isset to (xA+xB) and (yA+yB), respectively.

2.3.3.3 AF_MERGE Mode

When a CU is applied in AF_MERGE mode, it gets the first block codedwith affine mode from the valid neighbour reconstructed blocks. And theselection order for the candidate block is from left, above, aboveright, left bottom to above left as shown in FIG. 21A (denoted by A, B,C, D, E in order). For example, if the neighbour left bottom block iscoded in affine mode as denoted by A0 in FIG. 21B, the Control Point(CP) motion vectors mv₀ ^(N), mv₁ ^(N) and mv₂ ^(N) of the top leftcorner, above right corner and left bottom corner of the neighbouringCU/PU which contains the block A are fetched. And the motion vector mv₀^(C), mv₁ ^(C) and mv₂ ^(C) (which is only used for the 6-parameteraffine model) of the top left corner/top right/bottom left on thecurrent CU/PU is calculated based on mv₀ ^(N), mv₁ ^(N) and mv₂ ^(N). Itshould be noted that in VTM-2.0, sub-block (e.g. 4×4 block in VTM)located at the top-left corner stores mv0, the sub-block located at thetop-right corner stores mv₁ if the current block is affine coded. If thecurrent block is coded with the 6-parameter affine model, the sub-blocklocated at the bottom-left corner stores mv2; otherwise (with the4-parameter affine model), LB stores mv2′. Other sub-blocks stores theMVs used for MC.

After the CPMV of the current CU mv₀ ^(C), mv₁ ^(C) and mv₂ ^(C) arederived, according to the simplified affine motion model Equation (1)and (2), the MVF of the current CU is generated. In order to identifywhether the current CU is coded with AF_MERGE mode, an affine flag issignalled in the bitstream when there is at least one neighbour block iscoded in affine mode.

In some existing implementations, an affine merge candidate list isconstructed with following steps:

1) Insert Inherited Affine Candidates

Inherited affine candidate means that the candidate is derived from theaffine motion model of its valid neighbor affine coded block. Themaximum two inherited affine candidates are derived from affine motionmodel of the neighboring blocks and inserted into the candidate list.For the left predictor, the scan order is {A0, A1}; for the abovepredictor, the scan order is {B0, B1, B2}.

2) Insert Constructed Affine Candidates

If the number of candidates in affine merge candidate list is less thanMaxNumAffineCand (e.g., 5), constructed affine candidates are insertedinto the candidate list.

Constructed affine candidate means the candidate is constructed bycombining the neighbor motion information of each control point.

-   -   a) The motion information for the control points is derived        firstly from the specified spatial neighbors and temporal        neighbor shown in FIG. 22. CPk (k=1, 2, 3, 4) represents the        k-th control point. A0, A1, A2, B0, B1, B2 and B3 are spatial        positions for predicting CPk (k=1, 2, 3); T is temporal position        for predicting CP4.        -   The coordinates of CP1, CP2, CP3 and CP4 is (0, 0), (W, 0),            (H, 0) and (W, H), respectively, where W and H are the width            and height of current block.

The motion information of each control point is obtained according tothe following priority order:

-   -   For CP1, the checking priority is B2->B3->A2. B2 is used if it        is available. Otherwise, if B2 is available, B3 is used. If both        B2 and B3 are unavailable, A2 is used. If all the three        candidates are unavailable, the motion information of CP1 cannot        be obtained.    -   For CP2, the checking priority is B1->B0.    -   For CP3, the checking priority is A1->A0.    -   For CP4, T is used.    -   b) Secondly, the combinations of controls points are used to        construct an affine merge candidate.        -   I. Motion information of three control points are needed to            construct a 6-parameter affine candidate. The three control            points can be selected from one of the following four            combinations ({CP1, CP2, CP4}, {CP1, CP2, CP3}, {CP2, CP3,            CP4}, {CP1, CP3, CP4}). Combinations {CP1, CP2, CP3}, {CP2,            CP3, CP4}, {CP1, CP3, CP4} will be converted to a            6-parameter motion model represented by top-left, top-right            and bottom-left control points.        -   II. Motion information of two control points are needed to            construct a 4-parameter affine candidate. The two control            points can be selected from one of the two combinations            ({CP1, CP2}, {CP1, CP3}). The two combinations will be            converted to a 4-parameter motion model represented by            top-left and top-right control points.        -   III. The combinations of constructed affine candidates are            inserted into to candidate list as following order: {CP1,            CP2, CP3}, {CP1, CP2, CP4}, {CP1, CP3, CP4}, {CP2, CP3,            CP4}, {CP1, CP2}, {CP1, CP3}            -   i. For each combination, the reference indices of list X                for each CP are checked, if they are all the same, then                this combination has valid CPMVs for list X. If the                combination does not have valid CPMVs for both list 0                and list 1, then this combination is marked as invalid.                Otherwise, it is valid, and the CPMVs are put into the                sub-block merge list.                3) Padding with Zero Motion Vectors

If the number of candidates in affine merge candidate list is less than5, zero motion vectors with zero reference indices are insert into thecandidate list, until the list is full.

More specifically, for the sub-block merge candidate list, a 4-parametermerge candidate with MVs set to (0, 0) and prediction direction set touni-prediction from list 0 (for P slice) and bi-prediction (for Bslice).

2.3.4 Current Picture Referencing

Intra block copy (a.k.a. IBC, or intra picture block compensation), alsonamed current picture referencing (CPR) was adopted in HEVC screencontent coding extensions (SCC). This tool is very efficient for codingof screen content video in that repeated patterns in text and graphicsrich content occur frequently within the same picture. Having apreviously reconstructed block with equal or similar pattern as apredictor can effectively reduce the prediction error and thereforeimprove coding efficiency. An example of the intra block compensation isillustrated in FIG. 23.

Similar to the design of CRP in HEVC SCC, In VVC, The use of the IBCmode is signaled at both sequence and picture level. When the IBC modeis enabled at sequence parameter set (SPS), it can be enabled at picturelevel. When the IBC mode is enabled at picture level, the currentreconstructed picture is treated as a reference picture. Therefore, nosyntax change on block level is needed on top of the existing VVC intermode to signal the use of the IBC mode.

Main features:

-   -   It is treated as a normal inter mode. Therefore, merge and skip        modes are also available for the IBC mode. The merge candidate        list construction is unified, containing merge candidates from        the neighboring positions that are either coded in the IBC mode        or the HEVC inter mode. Depending on the selected merge index,        the current block under merge or skip mode can merge into either        an IBC mode coded neighbor or otherwise an normal inter mode        coded one with different pictures as reference pictures.    -   Block vector prediction and coding schemes for the IBC mode        reuse the schemes used for motion vector prediction and coding        in the HEVC inter mode (AMVP and MVD coding).    -   The motion vector for the IBC mode, also referred as block        vector, is coded with integer-pel precision, but stored in        memory in 1/16-pel precision after decoding as quarter-pel        precision is required in interpolation and deblocking stages.        When used in motion vector prediction for the IBC mode, the        stored vector predictor will be right shifted by 4.    -   Search range: it is restricted to be within the current CTU.    -   CPR is disallowed when affine mode/triangular mode/GBI/weighted        prediction is enabled.

2.3.5 Merge List Design in VVC

There are three different merge list construction processes supported inVVC:

-   -   1) Sub-block merge candidate list: it includes ATMVP and affine        merge candidates. One merge list construction process is shared        for both affine modes and ATMVP mode. Here, the ATMVP and affine        merge candidates may be added in order. Sub-block merge list        size is signaled in slice header, and maximum value is 5.    -   2) Uni-Prediction TPM merge list: For triangular prediction        mode, one merge list construction process for the two partitions        is shared even two partitions could select their own merge        candidate index. When constructing this merge list, the spatial        neighbouring blocks and two temporal blocks of the block are        checked. The motion information derived from spatial neighbours        and temporal blocks are called regular motion candidates in our        IDF. These regular motion candidates are further utilized to        derive multiple TPM candidates. Please note the transform is        performed in the whole block level, even two partitions may use        different motion vectors for generating their own prediction        blocks. Uni-Prediction TPM merge list size is fixed to be 5.    -   3) Regular merge list: For remaining coding blocks, one merge        list construction process is shared. Here, the        spatial/temporal/HMVP, pairwise combined bi-prediction merge        candidates and zero motion candidates may be inserted in order.        Regular merge list size is signaled in slice header, and maximum        value is 6.        2.3.5.1 Sub-block merge candidate list

It is suggested that all the sub-block related motion candidates are putin a separate merge list in addition to the regular merge list fornon-sub block merge candidates.

The sub-block related motion candidates are put in a separate merge listis named as ‘sub-block merge candidate list’.

In one example, the sub-block merge candidate list includes affine mergecandidates, and ATMVP candidate, and/or sub-block based STMVP candidate.

2.3.5.1.1 Another ATMVP Embodiment

In this contribution, the ATMVP merge candidate in the normal merge listis moved to the first position of the affine merge list. Such that allthe merge candidates in the new list (i.e., sub-block based mergecandidate list) are based on sub-block coding tools.

2.3.5.1.2 ATMVP in VTM-3.0

In VTM-3.0, a special merge candidate list, known as sub-block mergecandidate list (a.k.a affine merge candidate list) is added besides theregular merge candidate list. The sub-block merge candidate list isfilled with candidates in the following order:

b. ATMVP candidate (maybe available or unavailable);

c. Inherited Affine candidates;

d. Constructed Affine candidates;

e. Padding as zero MV 4-parameter affine model

The maximum number of candidates (denoted as ML) in the sub-block mergecandidate list derived as below:

-   -   1) If the ATMVP usage flag (e.g. the flag may be named as        “sps_sbtmvp_enabled_flag”) is on (equal to 1), but the affine        usage flag (e.g. the flag may be named as        “sps_affine_enabled_flag”) is off (equal to 0), then ML is set        equal to 1.    -   2) If the ATMVP usage flag is off (equal to 0), and the affine        usage flag is off (equal to 0), then ML is set equal to 0. In        this case, the sub-block merge candidate list is not used.    -   3) Otherwise (the affine usage flag is on (equal to 1), the        ATMVP usage flag is on or off), ML is signaled from the encoder        to the decoder. Valid ML is 0<=ML<=5.

When construct the sub-block merge candidate list, ATMVP candidate ischecked first. If any one of the following conditions is true, ATMVPcandidate is skipped and not put into the sub-block merge candidatelist.

-   -   1) The ATMVP usage flag is off;    -   2) Any TMVP usage flag (e.g. the flag may be named as        “slice_temporal_mvp_enabled_flag” when signaled at slice level)        is off;    -   3) The reference picture with reference index 0 in reference        list 0 is identical to the current picture (It is a CPR)

ATMVP in VTM-3.0 is much simpler than in JEM. When an ATMVP mergecandidate is generated, the following process is applied:

-   -   a. Check neighbouring blocks A1, B1, B0, A0 as shown in FIG. 22        in order, to find the first inter-coded, but not CPR-coded        block, denoted as block X;    -   b. Initialize TMV=(0,0). If there is a MV (denoted as MV′) of        block X, referring to the collocated reference picture (as        signaled in the slice header), TMV is set equal to MV′.    -   c. Suppose the center point of the current block is (x0, y0),        then locate a corresponding position of (x0,y0) as M=(x0+MV′x,        y0+MV′y) in the collocated picture. Find the block Z covering M.        -   i. If Z is intra-coded, then ATMVP is unavailable;        -   ii. If Z is inter-coded, MVZ_0 and MVZ_1 for the two lists            of block Z are scaled to (Reflist 0 index 0) and (Reflist 1            index 0) as MVdefault0, MVdefault1, and stored.    -   d. For each 8×8 sub-block, suppose its center point is (x0S,        y0S), then locate a corresponding position of (x0S, y0S) as        MS=(x0S+MV′x, y0S+MV′y) in the collocated picture. Find the        block ZS covering MS.        -   i. If ZS is intra-coded, MVdefault0, MVdefault1 are assigned            to the sub-block;        -   ii. If ZS is inter-coded, MVZS_0 and MVZS_1 for the two            lists of block ZS are scaled to (Reflist 0 index 0) and            (Reflist 1 index 0) and are assigned to the sub-block;

MV Clipping and Masking in ATMVP:

When locating a corresponding position such as M or MS in the collocatedpicture, it is clipped to be inside a predefined region. The CTU size isS×S, S=128 in VTM-3.0. Suppose the top-left position of the collocatedCTU is (xCTU, yCTU), then the corresponding position M or MS at (xN, yN)will be clipped into the valid region xCTU<=xN<xCTU+S+4;yCTU<=yN<yCTU+S.

-   Besides Clipping, (xN, yN) is also masked as xNxN&MASK, yNyN&MASK,    where MASK is an integer equal to ˜(2^(N)−1), and N=3, to set the    lowest 3 bits to be 0. So xN and yN must be numbers which are times    of 8. (“˜” represents the bitwise complement operator).

FIG. 24 shows an example of a valid corresponding region in thecollocated picture.

2.3.5.1.3 Syntax Design in Slice Header

 if( sps_temporal_mvp_enabled_flag ) slice _(—) temporal _(—) mvp _(—)enabled _(—) flag u(1)  if( slice_type = = B ) mvd _(—) l1 _(—) zero_(—) flag u(1)  if( slice_temporal_mvp_enabled_flag ) { if( slice_type == B )  collocated _(—) from _(—) l0 _(—) flag u(1)  } ...if(!sps_affine_enabled_flag){  if(!sps_sbtmvp_enabled_flag)MaxSubBlockMergeListSize = 0 else MaxSubBlockMergeListSize = 1 } else{ five _(—) minus _(—) max _(—) num _(—) affine _(—) merge _(—) candue(v)  MaxSubBlockMergeListSize = 5- five_minus_max_num_affine_merge_cand }

2.3.5.2 Regular Merge List

Different from the merge list design, in VVC, the history-based motionvector prediction (HMVP) method is employed.

In HMVP, the previously coded motion information is stored. The motioninformation of a previously coded block is defined as an HMVP candidate.Multiple HMVP candidates are stored in a table, named as the HMVP table,and this table is maintained during the encoding/decoding processon-the-fly. The HMVP table is emptied when starting coding/decoding anew slice. Whenever there is an inter-coded block, the associated motioninformation is added to the last entry of the table as a new HMVPcandidate. The overall coding flow is depicted in FIG. 25.

HMVP candidates could be used in both AMVP and merge candidate listconstruction processes. FIG. 26 depicts the modified merge candidatelist construction process (highlighted in blue). When the mergecandidate list is not full after the TMVP candidate insertion, HMVPcandidates stored in the HMVP table could be utilized to fill in themerge candidate list.

Considering that one block usually has a higher correlation with thenearest neighbouring block in terms of motion information, the HMVPcandidates in the table are inserted in a descending order of indices.The last entry in the table is firstly added to the list, while thefirst entry is added in the end. Similarly, redundancy removal isapplied on the HMVP candidates. Once the total number of available mergecandidates reaches the maximal number of merge candidates allowed to besignaled, the merge candidate list construction process is terminated.

2.4 MV Rounding

In VVC, when MV is right shifted, it is asked to be rounded toward zero.In a formulated way, for a MV(MVx, MVy) to be right shifted with N bits,the result MV′(MVx′, MVy′) will be derived as:

MVx′=(MVx+((1<<N)>>1)−(MVx>=0?1:0))>>N;

MVy′=(MVy+((1<<N)>>1)−(MVy>=0?1:0))>>N;

2.5 Embodiments of Reference Picture Resampling (RPR)

ARC, a.k.a. reference picture resampling (RPR) has been incorporated insome existing and upcoming video standards.

In some embodiments of RPR, TMVP is disabled if the collocated picturehas a different resolution to the current picture. Besides, BDOF andDMVR are disabled when the reference picture has a different resolutionto the current picture.

To handle the normal MC when the reference picture has a differentresolution than the current picture, the interpolation section isdefined as below:

8.5.6.3 Fractional Sample Interpolation Process 8.5.6.3.1 General

Inputs to this process are:

-   -   a luma location (xSb, ySb) specifying the top-left sample of the        current coding subblock relative to the top-left luma sample of        the current picture,    -   a variable sbWidth specifying the width of the current coding        subblock,    -   a variable sbHeight specifying the height of the current coding        subblock,    -   a motion vector offset mvOffset,    -   a refined motion vector refMvLX,    -   the selected reference picture sample array refPicLX,    -   the half sample interpolation filter index hpelIfIdx,    -   the bi-directional optical flow flag bdofFlag,    -   a variable cIdx specifying the colour component index of the        current block.        Outputs of this process are:    -   an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array        predSamplesLX of prediction sample values.

The prediction block border extension size brdExtSize is derived asfollows:

brdExtSize=(bdofFlag∥(inter_affine_flag[xSb][ySb] &&sps_affine_prof_enabled_flag))?2:0  (8-752)

The variable fRefWidth is set equal to the PicOutputWidthL of thereference picture in luma samples.The variable fRefHeight is set equal to PicOutputHeightL of thereference picture in luma samples.The motion vector mvLX is set equal to (refMvLX−mvOffset).

-   -   If cIdx is equal to 0, the following applies:        -   The scaling factors and their fixed-point representations            are defined as

hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)

vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)

-   -   -   Let (xIntL, yIntL) be a luma location given in full-sample            units and (xFracL, yFracL) be an offset given in 1/16-sample            units. These variables are used only in this clause for            specifying fractional-sample locations inside the reference            sample arrays refPicLX.        -   The top-left coordinate of the bounding block for reference            sample padding (xSbInt_(L), ySbInt_(L)) is set equal to            (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).        -   For each luma sample location (x_(L)=0 . . .            sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)            inside the prediction luma sample array predSamplesLX, the            corresponding prediction luma sample value            predSamplesLX[x_(L)][y_(L)] is derived as follows:            -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be                luma locations pointed to by a motion vector                (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The                variables refxSb_(L), refx_(L), refySb_(L), and refy_(L)                are derived as follows:

refxSb _(L)=((xSb<<4)+refMvLX[0])*hori_scale_fp  (8-755)

refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x_(L)*((hori_scale_fp+8)>>4))+32)>>6  (8-756)

refySb _(L)=((ySb<<4)+refMvLX[1])*vert_scale_fp  (8-757)

refyL=((Sign(refySb)*((Abs(refySb)+128)>>8)+yL*((vert_scale_fp+8)>>4))+32)>>6  (8-758)

-   -   -   -   The variables XInt_(L), yInt_(L), xFrac_(L) and                yFrac_(L) are derived as follows:

xInt _(L) =refx _(L)>>4  (8-759)

yInt _(L) =refy _(L)>>4  (8-760)

xFrac _(L) =refx _(L) & 15  (8-761)

yFrac _(L) =refy _(L) & 15  (8-762)

-   -   -   If bdofFlag is equal to TRUE or            (sps_affine_prof_enabled_flag is equal to TRUE and            inter_affine_flag[xSb][ySb] is equal to TRUE), and one or            more of the following conditions are true, the prediction            luma sample value predSamplesLX[x_(L)][y_(L)] is derived by            invoking the luma integer sample fetching process as            specified in clause 8.5.6.3.3 with            (xInt_(L)+(xFrac_(L)>>3)−1), yInt_(L)+(yFrac_(L)>>3)−1) and            refPicLX as inputs.            -   1. x_(L) is equal to 0.            -   2. x_(L) is equal to sbWidth+1.            -   3. y_(L) is equal to 0.            -   4. y_(L) is equal to sbHeight+1.        -   Otherwise, the prediction luma sample value            predSamplesLX[xL][yL] is derived by invoking the luma sample            8-tap interpolation filtering process as specified in clause            8.5.6.3.2 with (xIntL−(brdExtSize>0?1:0),            yIntL−(brdExtSize>0?1:0)), (xFracL, yFracL), (xSbInt_(L),            ySbInt_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and            (xSb, ySb) as inputs.

    -   Otherwise (cIdx is not equal to 0), the following applies:        -   Let (xIntC, yIntC) be a chroma location given in full-sample            units and (xFracC, yFracC) be an offset given in 1/32 sample            units. These variables are used only in this clause for            specifying general fractional-sample locations inside the            reference sample arrays refPicLX.        -   The top-left coordinate of the bounding block for reference            sample padding (xSbIntC, ySbIntC) is set equal to            ((xSb/SubWidthC)+(mvLX[0]>>5),            (ySb/SubHeightC)+(mvLX[1]>>5)).        -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0            . . . sbHeight−1) inside the prediction chroma sample arrays            predSamplesLX, the corresponding prediction chroma sample            value predSamplesLX[xC][yC] is derived as follows:            -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be                chroma locations pointed to by a motion vector (mvLX[0],                mvLX[1]) given in 1/32-sample units. The variables                refxSb_(C), refySb_(C), refx_(C) and refy_(C) are                derived as follows:

refxSb _(C)=((xSb/SubWidthC<<5)+mvLX[0])*hori_scale_fp  (8-763)

refx _(C)=((Sign(refxSb _(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5  (8-764)

refySb _(C)=((ySb/SubHeightC<<5)+mvLX[1])*vert_scale_fp  (8-765)

refy _(C)=((Sign(refySb _(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5  (8-766)

-   -   -   -   The variables xInt_(C), yInt_(C), xFrac_(C) and                yFrac_(C) are derived as follows:

xInt _(C) =refx _(C)>>5  (8-767)

yInt _(C) =refy _(C)>>5  (8-768)

xFrac _(C) =refy _(C) & 31  (8-769)

yFrac _(C) =refy _(C) & 31  (8-770)

-   -   -   -   The prediction sample value predSamplesLX[xC][yC] is                derived by invoking the process specified in clause                8.5.6.3.4 with (xInt_(C), yInt_(C)), (xFrac_(C),                yFrac_(C)), (xSbIntC, ySbIntC), sbWidth, sbHeight and                refPicLX as inputs.

8.5.6.3.2 Luma Sample Interpolation Filtering Process

Inputs to this Process are:

-   -   a luma location in full-sample units (xInt_(L), yInt_(L)),    -   a luma location in fractional-sample units (xFrac_(L),        yFrac_(L)),    -   a luma location in full-sample units (xSbInt_(L), ySbInt_(L))        specifying the top-left sample of the bounding block for        reference sample padding relative to the top-left luma sample of        the reference picture,    -   the luma reference sample array refPicLx_(L),    -   the half sample interpolation filter index hpelIfIdx,    -   a variable sbWidth specifying the width of the current subblock,    -   a variable sbHeight specifying the height of the current        subblock,    -   a luma location (xSb, ySb) specifying the top-left sample of the        current subblock relative to the top-left luma sample of the        current picture,        Output of this process is a predicted luma sample value        predSampleLx_(L)        The variables shift1, shift2 and shift3 are derived as follows:    -   The variable shift1 is set equal to Min(4, BitDepth_(Y)−8), the        variable shift2 is set equal to 6 and the variable shift3 is set        equal to Max(2, 14−BitDepth_(Y)).    -   The variable picW is set equal to pic_width_in_luma_samples and        the variable picH is set equal to pic_height_in_luma_samples.        The luma interpolation filter coefficients f_(L)[p] for each        1/16 fractional sample position p equal to xFrac_(L) or        yFrac_(L) are derived as follows:    -   If MotionModelIdc[xSb][ySb] is greater than 0, and sbWidth and        sbHeight are both equal to 4, the luma interpolation filter        coefficients f_(L)[p] are specified in Table 8-12.    -   Otherwise, the luma interpolation filter coefficients f_(L)[p]        are specified in Table 8-11 depending on hpelIfIdx.

The luma locations in full-sample units (xInt_(i), yInt_(i)) are derivedas follows for i=0 . . . 7:

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xInt _(i)=Clip3(SubPicLeftBoundaryPos,SubPicRightBoundaryPos,xInt _(L)+i−3)  (8-771)

yInt _(i)=Clip3(SubPicTopBoundaryPos,SubPicBotBoundaryPos,yInt _(L)+i−3)  (8-772)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),        the following applies:

xInt_(i)=Clip3(0,picW−1,sps_ref_wraparound_enabled_flag?ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY,picW,xInt_(L) +i−3):xInt _(L) +i−3)   (8-773)

yInt _(i)=Clip3(0,picH−1,yInt _(L) +i−3)   (8-774)

The luma locations in full-sample units are further modified as followsfor i=0 . . . 7:

xInt _(i)=Clip3(xSbInt _(L)−3,xSbInt _(L)+sbWidth+4,xInt _(i))  (8-775)

yInt _(i)=Clip3(ySbInt _(L)−3,ySbInt _(L)+sbHeight+4,yInt _(i))  (8-776)

The predicted luma sample value predSampleLx_(L) is derived as follows:

-   -   If both xFrac_(L) and yFrac_(L) are equal to 0, the value of        predSampleLx_(L) is derived as follows:

predSampleLx _(L) =refPicLx _(L)[xInt ₃][yInt ₃]<<shift3  (8-777)

-   -   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is equal        to 0, the value of predSampleLx_(L) is derived as follows:

predSampleLx _(L)=(Σ_(i=0) ⁷ f _(L)[xFrac _(L)][i]*refPicLX _(L)[xInt_(i)][yInt ₃])>>shift1  (8-778)

-   -   Otherwise, if xFrac_(L) is equal to 0 and yFrac_(L) is not equal        to 0, the value of predSampleLx_(L) is derived as follows:

predSampleLx _(L)=(Σ_(i=0) ⁷ f _(L)[yFrac _(L)][i]*refPicLX _(L)[xInt₃][yInt _(i)])>shift1  (8-779)

-   -   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is not        equal to 0, the value of predSampleLx_(L) is derived as follows:        -   The sample array temp[n] with n=0.27, is derived as follows:

temp[n]=(Σ_(i=0) ⁷ f _(L)[xFrac _(L)][i]*refPicLX _(L)[xInt _(i)][yInt_(n)])>>shift1  (8-780)

-   -   -   The predicted luma sample value predSampleLx_(L) is derived            as follows:

predSampleLx _(L)=(Σ_(i=0) ⁷ f _(L)[yFrac_(L)][i]*temp[i])>>shift2  (8-781)

TABLE 8-11 Specification of the luma interpolation filter coefficientsf_(L)[ p ] for each 1/16 fractional sample position p. Fractional sampleinterpolation filter coefficients position p f_(L)[ p ][ 0 ] f_(L)[ p ][1 ] f_(L)[ p ][ 2 ] f_(L)[ p ][ 3 ] f_(L)[ p ][ 4 ] f_(L)[ p ][ 5 ]f_(L)[ p ][ 6 ] f_(L)[ p ][ 7 ] 1 0 1 −3 63 4 −2 1 0 2 −1 2 −5 62 8 −3 10 3 −1 3 −8 60 13 −4 1 0 4 −1 4 −10 58 17 −5 1 0 5 −1 4 −11 52 26 −8 3−1 6 −1 3 −9 47 31 −10 4 −1 7 −1 4 −11 45 34 −10 4 −1 8 −1 4 −11 40 40−11 4 −1 (hpelIfIdx = = 0) 8 0 3 9 20 20 9 3 0 (hpelIfIdx = = 1) 9 −1 4−10 34 45 −11 4 −1 10 −1 4 −10 31 47 −9 3 −1 11 −1 3 −8 26 52 −11 4 −112 0 1 −5 17 58 −10 4 −1 13 0 1 −4 13 60 −8 3 −1 14 0 1 −3 8 62 −5 2 −115 0 1 −2 4 63 −3 1 0

TABLE 8-12 Specification of the luma interpolation filter coefficientsf_(L)[ p ] for each 1/16 fractional sample position p for affine motionmode. Fractional sample interpolation filter coefficients position pf_(L)[ p ][ 0 ] f_(L)[ p ][ 1 ] f_(L)[ p ][ 2 ] f_(L)[ p ][ 3 ] f_(L)[ p][ 4 ] f_(L)[ p ][ 5 ] f_(L)[ p ][ 6 ] f_(L)[ p ][ 7 ] 1 0 1 −3 63 4 −21 0 2 0 1 −5 62 8 −3 1 0 3 0 2 −8 60 13 −4 1 0 4 0 3 −10 58 17 −5 1 0 50 3 −11 52 26 −8 2 0 6 0 2 −9 47 31 −10 3 0 7 0 3 −11 45 34 −10 3 0 8 03 −11 40 40 −11 3 0 9 0 3 −10 34 45 −11 3 0 10 0 3 −10 31 47 −9 2 0 11 02 −8 26 52 −11 3 0 12 0 1 −5 17 58 −10 3 0 13 0 1 −4 13 60 −8 2 0 14 0 1−3 8 62 −5 1 0 15 0 1 −2 4 63 −3 1 0

8.5.6.3.3 Luma Integer Sample Fetching Process

Inputs to this Process are:

-   -   a luma location in full-sample units (xnt_(L), yInt_(L)),    -   the luma reference sample array refPicLx_(L),        Output of this process is a predicted luma sample value        predSampleLx_(L)        The variable shift is set equal to Max(2, 14−BitDepth_(Y)).        The variable picW is set equal to pic_width_in_luma_samples and        the variable picH is set equal to pic_height_in_luma_samples.        The luma locations in full-sample units (xInt, yInt) are derived        as follows:

xInt=Clip3(0,picW−1,sps_ref_wraparound_enabled_flag?ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY,picW,xIntL):xInt_(L))  (8-782)

yInt=Clip3(0,picH−1,yInt _(L))  (8-783)

The predicted luma sample value predSampleLx_(L) is derived as follows:

predSampleLx _(L) =refPicLx _(L)[xInt][yInt]<<shift3   (8-784)

8.5.6.3.4 Chroma Sample Interpolation Process

Inputs to this Process are:

-   -   a chroma location in full-sample units (xInt_(C), yInt_(C)),    -   a chroma location in 1/32 fractional-sample units (xFrac_(C),        yFrac_(C)),    -   a chroma location in full-sample units (xSbIntC, ySbIntC)        specifying the top-left sample of the bounding block for        reference sample padding relative to the top-left chroma sample        of the reference picture,    -   a variable sbWidth specifying the width of the current subblock,    -   a variable sbHeight specifying the height of the current        subblock,    -   the chroma reference sample array refPicLX_(C).        Output of this process is a predicted chroma sample value        predSampleLX_(C)        The variables shift1, shift2 and shift3 are derived as follows:    -   The variable shift1 is set equal to Min(4, BitDepth_(C)−8), the        variable shift2 is set equal to 6 and the variable shift3 is set        equal to Max(2, 14−BitDepth_(C)).    -   The variable picW_(C) is set equal to        pic_width_in_luma_samples/SubWidthC and the variable picH_(C) is        set equal to pic_height_in_luma_samples/SubHeightC.        The chroma interpolation filter coefficients f_(C)[p] for each        1/32 fractional sample position p equal to xFrac_(C) or        yFrac_(C) are specified in Table 8-13.        The variable xOffset is set equal to        (sps_ref_wraparound_offset_minus1+1)*MinCbSizeY)/SubWidthC.        The chroma locations in full-sample units (xInt_(i), yInt_(i))        are derived as follows for i=0 . . . 3:    -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xint_(i)=Clip3(SubPicLeftBoundaryPos/SubWidthC,SubPicRightBoundaryPos/SubWidthC,xInt_(L) +i)  (8-785)

yInt_(i)=Clip3(SubPicTopBoundaryPos/SubHeightC,SubPicBotBoundaryPos/SubHeightC,yInt_(L) +i)  (8-786)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),        the following applies:

xInt _(i)=Clip3(0,picW_(C)−1,sps_ref_wraparound_enabled_flag?ClipH(xOffset,picW _(C) ,xInt_(C) +i−1):xInt _(C) +i−1)  (8-787)

yInt _(i)=Clip3(0,picH _(C)−1,yInt _(C) +i−1)   (8-788)

The chroma locations in full-sample units (xInt_(i), yInt_(i)) arefurther modified as follows for i=0 . . . 3:

xInt _(i)=Clip3(xSbIntC−1,xSbIntC+sbWidth+2,xInt _(i))  (8-789)

yInt _(i)=Clip3(ySbIntC−1,ySbIntC+sbHeight+2,yInt _(i))  (8-790)

The predicted chroma sample value predSampleLX_(C) is derived asfollows:

-   -   If both xFrac_(C) and yFrac_(C) are equal to 0, the value of        predSampleLX_(C) is derived as follows:

predSampleLX _(C) =refPicLX _(C)[xInt ₁][yInt ₁]<<shift3  (8-791)

-   -   Otherwise, if xFrac_(C) is not equal to 0 and yFrac_(C) is equal        to 0, the value of predSampleLX_(C) is derived as follows:

predSampleLX _(C)=(Σ_(i=0) ³ f _(C)[xFrac _(C)][i]*refPicLX _(C)[xnt_(i)][yInt ₁])>>shift1  (8-792)

-   -   Otherwise, if xFrac_(C) is equal to 0 and yFrac_(C) is not equal        to 0, the value of predSampleLX_(C) is derived as follows:

predSampleLX _(C)=(Σ_(i=0) ³ f _(C)[yFrac _(C)][i]*refPicLX _(C)[xInt₁][yInt _(i)])>>shift1  (8-793)

-   -   Otherwise, if xFrac_(C) is not equal to 0 and yFrac_(C) is not        equal to 0, the value of predSampleLX_(C) is derived as follows:        -   The sample array temp[n] with n=0 . . . 3, is derived as            follows:

temp[n]=(Σ_(i=0) ³ f _(C)[xFrac _(C)][i]*refPicLX _(C)[xInt _(i)][yInt_(n)])>>shift1  (8-794)

-   -   -   The predicted chroma sample value predSampleLX_(C) is            derived as follows:

predSampleLX _(C)=(f _(C)[yFrac _(C)][0]*temp[0]+f _(C)[yFrac_(C)][1]*temp[1]+f _(C)[yFrac _(C)][2]*temp[2]+f _(C)[yFrac_(C)][3]*temp[3])>>shift2  (8-795)

TABLE 8-13 Specification of the chroma interpolation filter coefficientsfc[ p ] for each 1/32 fractional sample position p. Fractional sampleinterpolation filter coefficients position p f_(C)[ p ][ 0 ] f_(C)[ p ][1 ] f_(C)[ p ][ 2 ] f_(C)[ p ][ 3 ] 1 −1 63 2 0 2 −2 62 4 0 3 −2 60 7 −14 −2 58 10 −2 5 −3 57 12 −2 6 −4 56 14 −2 7 −4 55 15 −2 8 −4 54 16 −2 9−5 53 18 −2 10 −6 52 20 −2 11 −6 49 24 −3 12 −6 46 28 −4 13 −5 44 29 −414 −4 42 30 −4 15 −4 39 33 −4 16 −4 36 36 −4 17 −4 33 39 −4 18 −4 30 42−4 19 −4 29 44 −5 20 −4 28 46 −6 21 −3 24 49 −6 22 −2 20 52 −6 23 −2 1853 −5 24 −2 16 54 −4 25 −2 15 55 −4 26 −2 14 56 −4 27 −2 12 57 −3 28 −210 58 −2 29 −1 7 60 −2 30 0 4 62 −2 31 0 2 63 −1

2.6 Embodiments Employing Sub-Pictures

With the current syntax design of sub-pictures in an existingimplementation, the locations and dimensions of sub-pictures are derivedas below:

subpics _(—) present _(—) flag u(1) if( subpics_present_flag ) { max_(—) subpics _(—) minus1 u(8) subpic _(—) grid _(—) col _(—) width _(—)minus1 u(v) subpic _(—) grid _(—) row _(—) height _(—) minus1 u(v) for(i = 0; i < NumSubPicGridRows; i++ ) for( j = 0; j < NumSubPicGridCols;j++ ) subpic _(—) grid _(—) idx[ i ][ j ] u(v) for( i = 0; i <=NumSubPics; i++ ) { subpic _(—) treated _(—) as _(—) pic _(—) flag[ i ]u(1) loop _(—) filter _(—) across _(—) subpic _(—) enabled _(—) flag[ i] u(1) } }subpics_present_flag equal to 1 indicates that subpicture parameters arepresent in the present in the SPS RBSP syntax. subpics_present_flagequal to 0 indicates that subpicture parameters are not present in thepresent in the SPS RBSP syntax.

-   -   NOTE 2—When a bitstream is the result of a sub-bitstream        extraction process and contains only a subset of the subpictures        of the input bitstream to the sub-bitstream extraction process,        it might be required to set the value of subpics_present_flag        equal to 1 in the RBSP of the SPSs.        max_subpics_minus1 plus 1 specifies the maximum number of        subpictures that may be present in the CVS. max_subpics_minus1        shall be in the range of 0 to 254. The value of 255 is reserved        for future use by ITU-T|ISO/IEC.        subpic_grid_col_width_minus1 plus 1 specifies the width of each        element of the subpicture identifier grid in units of 4 samples.        The length of the syntax element is Ceil(Log        2(pic_width_max_in_luma_samples/4)) bits.        The variable NumSubPicGridCols is derived as follows:

NumSubPicGridCols=(pic_width_max_in_luma_samples+subpic_grid_col_width_minus1*4+3)/(subpic_grid_col_width_minus1*4+4)  (7-5)

subpic_grid_row_height_minus1 plus 1 specifies the height of eachelement of the subpicture identifier grid in units of 4 samples. Thelength of the syntax element is Ceil(Log2(pic_height_max_in_luma_samples/4)) bits.The variable NumSubPicGridRows is derived as follows:

NumSubPicGridRows=(pic_height_max_in_luma_samples+subpic_grid_row_height_minus1*4+3)/(subpic_grid_row_height_minus1*4+4)  (7-6)

subpic_grid_idx[i][j] specifies the subpicture index of the gridposition (i, j). The length of the syntax element is Ceil(Log2(max_subpics_minus1+1)) bits.The variables SubPicTop[subpic_grid_idx[i][j]],SubPicLeft[subpic_grid_idx[i][j]], SubPicWidth[subpic_grid_idx[i][j]],SubPicHeight[subpic_grid_idx[i][j]], and NumSubPics are derived asfollows:

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) { for( j = 0; j< NumSubPicGridCols; j++ ) { if ( i = = 0) SubPicTop[ subpic_grid_idx[ i][ j ] ] = 0 else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i −1 ][ j ] ) { SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i SubPicHeight[subpic_grid_idx[ i − 1 ][ j ] ] = i − SubPicTop[ subpic_grid_idxi[ i − 1][ j ] ] } if ( j = = 0) SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0(7-7) else if (subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1] ) { SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j SubPicWidth[subpic_grid_idx[ i ][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j −1 ] ] } if ( i = = NumSubPicGridRows − 1) SubPicHeight[ subpic_grid_idx[i ][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ] + 1 if (j == NumSubPicGridRows − 1) SubPicWidth[ subpic_grid_idx[ i ][ j ] ] = j −SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ] + 1 if( subpic_grid_idx[ i][ j ] > NumSubPics)  NumSubPics = subpic_grid_idx[ i ][ j ] } }subpic_treated_as_pic_flag[i] equal to 1 specifies that the i-thsubpicture of each coded picture in the CVS is treated as a picture inthe decoding process excluding in-loop filtering operations.subpic_treated_as_pic_flag[i] equal to 0 specifies that the i-thsubpicture of each coded picture in the CVS is not treated as a picturein the decoding process excluding in-loop filtering operations. When notpresent, the value of subpic_treated_as_pic_flag[i] is inferred to beequal to 0.

2.7 Combined Inter-Intra Prediction (CIIP)

Combined Inter-Intra Prediction (CIIP) is adopted into VVC as a specialmerge candidate. It can only be enabled for a W×H block with W<=64 andH<=64.

3. Drawbacks of Existing Implementations

In the current design of VVC, ATMVP has following problems:

-   -   1) Whether to apply ATMVP is mismatched in slice level and in CU        level;    -   2) In slice header, ATMVP may be enabled even if TMVP is        disabled. Meanwhile, ATMVP flag is signaled before TMVP flag.    -   3) Masking is always done without considering whether MV is        compressed;    -   4) The valid corresponding region may be too large;    -   5) The derivation of TMV is too complicated;    -   6) ATMVP may be unavailable in some cases and a better default        MV is desirable.    -   7) The MV scaling methods in ATMVP may not be efficient;    -   8) ATMVP should consider the CPR cases;    -   9) A default zero affine merge candidate may be put into the        list even when affine prediction is disabled.    -   10) Current picture is treated as a long-term reference picture        while other pictures are treated as short-reference picture. For        both ATMVP and TMVP candidates, the motion information from a        temporal block in the collocated picture will be scaled to a        reference picture with fixed reference index (i.e., 0 for each        reference picture list in the current design). However, when CPR        mode is enabled, the current picture is also treated as a        reference picture and the current picture may be added to the        reference picture list 0 (RefPicList0) with index equal to 0.        -   a. For TMVP, if the temporal block is coded with CPR mode            and reference picture of RefPicList0 is a short reference            picture, the TMVP candidate is set to be unavailable.        -   b. If the reference picture of the RefPicList0 with index            equal to 0 is the current picture and current picture is the            Intra Random Access Point (IRAP) picture, ATMVP candidate is            set to be unavailable.        -   c. For a ATMVP sub-block within a block, when deriving the            sub-block's motion information from a temporal block, if the            temporal block is coded with CPR mode, default ATMVP            candidate (derived from a temporal block identified by the            starting TMV and center position of the current block) is            used to fill in the sub-block' motion information.    -   11) MV is right shifted to the integer precision, but not        following the rounding rule in VVC.    -   12) The MV(MV_(x), MV_(y)) used in ATMVP to locate a        corresponding block in a different picture (e.g., the TMV in 0)        is directly used since it points to the collocated picture. This        is based on the assumption that all pictures are in the same        resolution. However, when RPR is enabled, different picture        resolutions may be utilized. Similar issues are existing for        identification of corresponding blocks in a collocate picture to        derive sub-block motion information.    -   13) If one block width or height is greater than 32, and max        transform block size is 32, for a CIIP coded block, the intra        prediction signal is generated with the CU size; while the inter        prediction signal is generated with the TU size (recursively        splitting current block to multiple 32×32 blocks). Using the CU        to derive intra prediction signal results in less efficiency.        There are some problems with current design. Firstly, if the        reference picture of the RefPicList0 with index equal to 0 is        the current picture and current picture is not an IRAP picture,        ATMVP procedure is still invoked, but it couldn't find any        available ATMVP candidates since none of temporal motion vectors        could be scaled to the current picture.

4. Examples of Embodiments and Techniques

The itemized list of techniques and embodiments below should beconsidered as examples to explain general concepts. These techniquesshould not be interpreted in a narrow way. Furthermore, these techniquescan be combined in any manner in encoder or decoder embodiments.

-   -   1. Whether TMVP is allowed and/or whether CPR is used should be        considered to decide/parse the maximum number of candidates in        the sub-block merge candidate list and/or to decide whether        ATMVP candidate should be added to a candidate list. The maximum        number of candidates in the sub-block merge candidate list is        denoted as ML.        -   a) In one example, ATMVP is inferred to be not applicable if            either ATMVP usage flag is off (equal to 0), or TMVP is            disabled, in the determination of or parsing the maximum            number of candidates in the sub-block merge candidate list.            -   i. In one example, the ATMVP usage flag is on (equal                to 1) and TMVP is disabled, the ATMVP candidate is not                added to the sub-block merge candidate list or the ATMVP                candidate list.            -   ii. In one example, the ATMVP usage flag is on (equal                to 1) and TMVP is disabled, and the affine usage flag is                off (equal to 0), then ML is set equal to 0, meaning                that sub-block merge is not applicable.            -   iii. In one example, the ATMVP usage flag is on (equal                to 1) and TMVP is enabled, and the affine usage flag is                off (equal to 0), then ML is set equal to 1.        -   b) In one example, ATMVP is inferred to be not applicable if            either ATMVP usage flag is off (equal to 0), or the            collocated reference picture of the current picture is the            current picture itself, when decide or parse the maximum            number of candidates in the sub-block merge candidate list.            -   i. In one example, the ATMVP usage flag is on (equal                to 1) and the collocated reference picture of the                current picture is the current picture itself, the ATMVP                candidate is not added to the sub-block merge candidate                list or the ATMVP candidate list.            -   ii. In one example, the ATMVP usage flag is on (equal to                1), and the collocated reference picture of the current                picture is the current picture itself, and the affine                usage flag is off (equal to 0), then ML is set equal to                0, meaning that sub-block merge is not applicable.            -   iii. In one example, the ATMVP usage flag is on (equal                to 1), and the collocated reference picture of the                current picture is not the current picture itself, and                the affine usage flag is off (equal to 0), then ML is                set equal to 1.        -   c) In one example, ATMVP is inferred to be not applicable if            ATMVP usage flag is off (equal to 0), or the reference            picture with reference picture index 0 in reference list 0            is the current picture itself, when decide or parse the            maximum number of candidates in the sub-block merge            candidate list.            -   i. In one example, the ATMVP usage flag is on (equal                to 1) and the collocated reference picture with                reference picture index 0 in reference list 0 is the                current picture itself, the ATMVP candidate is not added                to the sub-block merge candidate list or the ATMVP                candidate list.            -   ii. In one example, the ATMVP usage flag is on (equal to                1), and the reference picture with reference picture                index 0 in reference list 0 is the current picture                itself, and the affine usage flag is off (equal to 0),                then ML is set equal to 0, meaning that sub-block merge                is not applicable.            -   iii. In one example, the ATMVP usage flag is on (equal                to 1) and the reference picture with reference picture                index 0 in reference list 0 is not the current picture                itself, and the affine usage flag is off (equal to 0),                then ML is set equal to 1.        -   d) In one example, ATMVP is inferred to be not applicable if            ATMVP usage flag is off (equal to 0), or the reference            picture with reference picture index 0 in reference list 1            is the current picture itself, when decide or parse the            maximum number of candidates in the sub-block merge            candidate list.            -   i. In one example, the ATMVP usage flag is on (equal                to 1) and the collocated reference picture with                reference picture index 0 in reference list 1 is the                current picture itself, the ATMVP candidate is not added                to the sub-block merge candidate list or the ATMVP                candidate list.            -   ii. In one example, the ATMVP usage flag is on (equal to                1), and the reference picture with reference picture                index 0 in reference list 1 is the current picture                itself, and the affine usage flag is off (equal to 0),                then ML is set equal to 0, meaning that sub-block merge                is not applicable.            -   iii. In one example, the ATMVP usage flag is on (equal                to 1) and the reference picture with reference picture                index 0 in reference list 1 is not the current picture                itself, and the affine usage flag is off (equal to 0),                then ML is set equal to 1.    -   2. It is proposed that ATMVP is disabled implicitly and no ATMVP        flag is signaled if TMVP is disabled at slice/tile/picture        level.        -   a) In one example, ATMVP flag is signaled after the TMVP            flag in slice header/tile header/PPS.        -   b) In one example, ATMVP or/and TMVP flag may be not            signaled in slice header/tile header/PPS and is only            signaled in SPS header.    -   3. Whether and how to do mask the corresponding position in        ATMVP depends on whether and how MVs are compressed. Suppose        (xN, yN) is a corresponding position calculated with the        coordinator of current block/sub-block and a starting motion        vector (e.g., TMV) in the collocated picture        -   a) In one example, (xN, yN) is not masked if MVs are not            required to be compressed (e.g.            sps_disable_motioncompression signaled in SPS is 1);            Otherwise, (MVs are required to be compressed) (xN, yN) is            masked as xN=xN&MASK, yN=yN& MASK, where MASK is an integer            equal to ˜(2^(M)−1), and M can be integers such as 3 or 4.        -   b) Assume the MV compression method for MV storage result in            each 2^(K)×2^(K) block share the same motion information and            the mask in the ATMVP process is defined as ˜(2^(M)−1). It            is proposed that K may be unequal to M, e.g., M=K+1.        -   c) The MASK used in ATMVP and TMVP maybe the same, or they            maybe different.    -   4. In one example, the MV compression method can be flexible.        -   a) In one example, the MV compression method can be selected            between no compression, 8×8 compression (M=3 in Bullet 3.a),            or 16×16 compression (M=4 in Bullet 3.a)        -   b) In one example, the MV compression method may be signaled            in VPS/SPS/PPS/slice header/tile group header.        -   c) In one example, the MV compression method can be set            differently in different standard profiles/levels/tiers.    -   5. The valid corresponding region in ATMVP may adaptive;        -   a) For example, the valid corresponding region may depend on            the width and height of the current block;        -   b) For example, the valid corresponding region may depend on            the MV compression method;            -   i. In one example, the valid corresponding region is                smaller if MV compression method is not used; the valid                corresponding region is larger if MV compression method                is used.    -   6. The valid corresponding region in ATMVP may be based on a        basic region with size M×N smaller than a CTU region. For        example, the CTU size in VTM-3.0 is 128×128, and the basic        region size may be 64×64. Suppose the width and height of the        current block is W and H.        -   a) In one example, if W<=M and H<=N, meaning that the            current block is inside a basic region, then the valid            corresponding region in ATMVP is the collocated basic region            and the extension in the collocated picture. FIG. 27 shows            an example.            -   i. For example, suppose the top-left position of the                collocated basic region is (xBR, yBR), then the                corresponding position at (xN, yN) will be clipped into                the valid region xBR<=xN<xBR+M+4; yBR<=yN<yBR+N.

FIG. 27 shows an example embodiment of the proposed valid region whenthe current block is inside a Basic Region (BR).

FIG. 28 shows an example embodiment of a valid region when the currentblock is not inside a basic region.

-   -   b) In one example, if W>M and H>N, meaning that the current        block is not inside a basic region, then the current block is        divided into several parts. Each part has an individual valid        corresponding region in ATMVP. For a position A in the current        block, its corresponding position B in the collocated block        should be within the valid corresponding region of the part in        which the position A locates.        -   i. For example, the current block is divided into            non-overlapped basic regions. The valid corresponding region            for one basic region is its collocated basic region and the            extension in the collocated picture. FIG. 28 shows an            example.            -   1. For example, suppose position A in the current block                is in one basic region R. The collocated basic region of                R in the collocated picture is denoted as CR. The                corresponding position of A in the collocated block is                position B. The top-left position of CR is (xCR, yCR),                then position B at (xN, yN) will be clipped into the                valid region xCR<=xN<xCR+M+4; yCR<=yN<yCR+N.    -   7. It is proposed the motion vector used in ATMVP to locate a        corresponding block in a different picture (e.g., the TMV in        2.3.5.1.2) can be derived as:        -   a) In one example, TMV is always set equal to a default MV            such as (0, 0).            -   i. In one example, the default MV is signaled in                VPS/SPS/PPS/slice header/tile group header/CTU/CU.        -   b) In one example, TMV is set to be one MV stored in the            HMVP table with the following methods;            -   i. If HMVP list is empty, TMV is set equal to a default                MV such as (0, 0)            -   ii. Otherwise (HMVP list is not empty),                -   1. TMV may be set to equal to the first element                    stored in the HMVP table;                -   2. Alternatively, TMV may be set to equal to the                    last element stored in the HMVP table;                -   3. Alternatively, TMV may only be set equal to a                    specific MV stored in the HMVP table;                -    a. In one example, the specific MV refers to                    reference list 0.                -    b. In one example, the specific MV refers to                    reference list 1.                -    c. In one example, the specific MV refers to a                    specific reference picture in reference list 0, such                    as the reference picture with index 0.                -    d. In one example, the specific MV refers to a                    specific reference picture in reference list 1, such                    as the reference picture with index 0.                -    e. In one example, the specific MV refers to the                    collocated picture.                -   4. Alternatively, TMV may be set equal to the                    default MV if the specific MV (e.g., mentioned in                    bullet 3.) stored in the HMVP table cannot be found;                -    a. In one example, only the first element stored in                    the HMVP table is searched to find the specific MV.                -    b. In one example, only the last element stored in                    the HMVP table is searched to find the specific MV.                -    c. In one example, some or all elements stored in                    the HMVP table is searched to find the specific MV.                -   5. Alternatively, furthermore, TMV obtained from the                    HMVP cannot refer to the current picture itself.                -   6. Alternatively, furthermore, TMV obtained from the                    HMVP table may be scaled to the collocated picture                    if it does not refer to it.        -   c) In one example, TMV is set to be one MV of one specific            neighbouring block. No other neighbouring blocks are            involved.            -   i. The specific neighbouring block may be block A0, A1,                B0, B1, B2 in FIG. 22.            -   ii. TMV may be set equal to the default MV if                -   1. The specific neighbouring block does not exist;                -   2. The specific neighbouring block is not                    inter-coded;            -   iii. TMV may only be set equal to a specific MV stored                in the specific neighbouring block;                -   1. In one example, the specific MV refers to                    reference list 0.                -   2. In one example, the specific MV refers to                    reference list 1.                -   3. In one example, the specific MV refers to a                    specific reference picture in reference list 0, such                    as the reference picture with index 0.                -   4. In one example, the specific MV refers to a                    specific reference picture in reference list 1, such                    as the reference picture with index 0.                -   5. In one example, the specific MV refers to the                    collocated picture.                -   6. TMV may be set equal to the default MV if the                    specific MV stored in the specific neighbouring                    block cannot be found;            -   iv. TMV obtained from the specific neighbouring block                may be scaled to the collocated picture if it does not                refer to it.            -   v. TMV obtained from the specific neighbouring block                cannot refer to the current picture itself.    -   8. MVdefault0 and MVdefault1 used in ATMVP as disclosed in        2.3.5.1.2 may be derived as        -   a) In one example, MVdefault0 and MVdefault1 are set equal            to (0,0);        -   b) In one example, MVdefaultX (X=0 or 1) is derived from            HMVP,            -   i. If HMVP list is empty, MVdefaultX is set equal to a                predefined default MV such as (0, 0).                -   1. The predefined default MV may be signaled in                    VPS/SPS/PPS/slice header/tile group header/CTU/CU.            -   ii. Otherwise (HMVP list is not empty),                -   1. MVdefaultX may be set to equal to the first                    element stored in the HMVP table;                -   2. MVdefaultX may be set to equal to the last                    element stored in the HMVP table;                -   3. MVdefaultX may only be set equal to a specific MV                    stored in the HMVP table;                -    a. In one example, the specific MV refers to                    reference list X.                -    b. In one example, the specific MV refers to a                    specific reference picture in reference list X, such                    as the reference picture with index 0.                -   4. MVdefaultX may be set equal to the predefined                    default MV if the specific MV stored in the HMVP                    table cannot be found;                -    a. In one example, only the first element stored in                    the HMVP table is searched.                -    b. In one example, only the last element stored in                    the HMVP table is searched.                -    c. In one example, some or all elements stored in                    the HMVP table is searched.                -   5. MVdefaultX obtained from the HMVP table may be                    scaled to the collocated picture if it does not                    refer to it.                -   6. MVdefaultX obtained from the HMVP cannot refer to                    the current picture itself.        -   c) In one example, MVdefaultX (X=0 or 1) is derived from a            neighbouring block.            -   i. The neighbouring blocks may include block A0, A1, B0,                B1, B2 in FIG. 22.                -   1. For example, only one of these blocks is used to                    derive MVdefaultX.                -   2. Alternatively, some or all of these blocks are                    used to derive MVdefaultX.                -    a. These blocks are checked in order until a valid                    MVdefaultX is found.                -   3. If no valid MVdefaultX can be found from selected                    one or more neighbouring blocks, it is set equal to                    a predefined default MV such as (0, 0).                -    a. The predefined default MV may be signaled in                    VPS/SPS/PPS/slice header/tile group header/CTU/CU.            -   ii. No valid MVdefaultX can be found from a specific                neighbouring block if                -   1. The specific neighbouring block does not exist;                -   2. The specific neighbouring block is not                    inter-coded;            -   iii. MVdefaultX may only be set equal to a specific MV                stored in the specific neighbouring block;                -   1. In one example, the specific MV refers to                    reference list X.                -   2. In one example, the specific MV refers to a                    specific reference picture in reference list X.,                    such as the reference picture with index 0            -   iv. MVdefaultX obtained from the specific neighbouring                block may be scaled to a specific reference picture,                such as the reference picture with index 0 in reference                list X.            -   v. MVdefaultX obtained from the specific neighbouring                block cannot refer to the current picture itself.    -   9. For either sub-block or non-sub-block ATMVP candidate, if a        temporal block for a sub-block/whole block in the collocated        picture is coded with CPR mode, a default motion candidate may        be utilized instead.        -   a) In one example, the default motion candidate may be            defined as the motion candidate associated with the center            position of current block (e.g., MVdefault0 and/or            MVdefault1 used in ATMVP as disclosed in 2.3.5.1.2).        -   b) In one example, the default motion candidate may be            defined as (0, 0) motion vector and reference picture index            equal to 0 for both reference picture lists, if available.    -   10. It is proposed that the default motion information for the        ATMVP process (e.g., MVdefault0 and MVdefault1 used in ATMVP as        disclosed in 2.3.5.1.2) may be derived based on the location of        a position that is used in the sub-block motion information        derivation process. With this proposed method, for that        sub-block, there is no need to further derive motion information        since the default motion information will be directly assigned.        -   a) In one example, instead of using the center position of            the current block, the center position of a sub-block (e.g.,            a center sub-block) within the current block may be            utilized.        -   b) An example of existing and proposed implementations are            shown in FIGS. 29A and 29B, respectively.    -   11. It is proposed that the ATMVP candidate is always available        with the following methods:        -   a) Suppose the center point of the current block is (x0,            y0), then locate a corresponding position of (x0,y0) as            M=(x0+MV′x, y0+MV′y) in the collocated picture. Find the            block Z covering M. If Z is intra-coded, then MVdefault0,            MVdefault1 are derived by some methods proposed in Item 6.        -   b) Alternatively, Block Z is not located to get the motion            information, some methods proposed in Item 8 are directly            applied to get MVdefault0 and MVdefault1.        -   c) Alternatively, the default motion candidate used in ATMVP            process is always available. If it is set to unavailable            based on current design (e.g., the temporal block is intra            coded), other motion vectors may be utilized instead for the            default motion candidate.            -   i. In one example, the solutions in international                application PCT/CN2018/124639, incorporated by reference                herein, may be applied.        -   d) Alternatively, furthermore, whether ATMVP candidate is            always available depend on other high-level syntax            information.            -   i. In one example, only when the ATMVP enabling flag at                slice/tile/picture header or other video units is set to                true is inferred to be true, the ATMVP candidate may be                always set to be available.            -   ii. In one example, the above methods may be only                applicable when ATMVP enabling flag in slice                header/picture header or other video units is set to                true and current picture is not an IRAP picture and                current picture is not inserted to RefPicList0 with                reference index equal to 0.        -   e) A fixed index or a fixed group of indices is assigned to            ATMVP candidates. When ATMVP candidates are always            unavailable, the fixed index/group index may be inferred to            other kinds of motion candidates (such as affine            candidates).    -   12. It is proposed that whether the Zero motion affine merge        candidate is put into the sub-block merge candidate list should        depend on whether affine prediction is enabled.        -   a) For example, if affine usage flag is off            (sps_affine_enabled_flag is equal to 0), the Zero motion            affine merge candidate is not put into the sub-block merge            candidate list.        -   b) Alternatively, furthermore, default motion vector            candidates which are non-affine candidate are added instead.    -   13. It is proposed that non-affine padding candidate may be put        into the sub-block merge candidate list.        -   a) Zero motion non-affine padding candidate may be added if            the sub-block merge candidate list is not fulfilled.        -   b) When such a padding candidate is chosen, the affine_flag            of the current block should be set to be 0.        -   c) Alternatively, Zero motion non-affine padding candidate            is put into the sub-block merge candidate list if the            sub-block merge candidate list is not fulfilled and affine            usage flag is off.    -   14. Suppose MV0 and MV1 represent the MVs in reference list 0        and reference list 1 of the block covering a corresponding        position (e.g., MV0 and MV1 may be MVZ_0 and MVZ_1 or MVZS_0 and        MVZS_1 described in section 2.3.5.1.2). MV0′ and MV1′ represent        the MVs in reference list 0 and reference list 1 to be derived        for the current block or sub-block. Then the MV0′ and MV1′        should be derived by scaling.        -   a) MV0, if the collocated picture is in reference list 1;        -   b) MV1, if the collocated picture is in reference list 0.    -   15. The ATMVP and/or TMVP enabling/disabling flag may be        inferred to be false for a slice/tile or other kinds of video        units when current picture is treated as a reference picture        with index set to M (e.g., 0) in a reference picture list X        (PicRefListX, e.g., X=0). Here, M may be equal to the target        reference picture index that motion information of a temporal        block shall be scaled to for PicRefListX during ATMVP/TMVP        processes.        -   a) Alternatively, furthermore, the above method is only            applicable when the current picture is an Intra Random            Access Point (IRAP) picture.        -   b) In one example, ATMVP and/or TMVP enabling/disabling flag            may be inferred to be false when current picture is treated            as a reference picture with index set to M (e.g., 0) in a            PicRefListX and/or current picture is treated as a reference            picture with index set to N (e.g., 0) in a PicRefListY. The            variable M and N represent the target reference picture            index used in TMVP or ATMVP process.        -   c) For the ATMVP process, it is restricted that a confirming            bitstream shall follow the rule that the collocated picture            wherein motion information of current block is derived from            shall not be the current picture.        -   d) Alternatively, when the above conditions are true, the            ATMVP or TMVP process is not invoked.    -   16. It is proposed that if a reference picture with index set to        M (e.g., 0) in a reference picture list X (PicRefListX, e.g.,        X=0) for the current block is the current picture, ATMVP may be        still enabled for this block.        -   a) In one example, all sub-blocks' motion information are            point to the current picture.        -   b) In one example, when obtaining the sub-block's motion            information from a temporal block, the temporal block shall            be coded with at least one reference picture pointing to the            current picture of the temporal block.        -   c) In one example, when obtaining the sub-block's motion            information from a temporal block, no scaling operations are            applied.    -   17. Coding methods of sub-block merge index are aligned        regardless the usage of ATMVP or not.        -   a) In one example, for the first L bins, they are context            coded. For the remaining bins, they are bypass coded. In one            example, L is set to 1.        -   b) Alternatively, for all bins, they are context coded.    -   18. The MV(MV_(x), MV_(y)) used in ATMVP to locate a        corresponding block in a different picture (e.g., the TMV in 0)        may be right-shifted to the integer precision (denoted as (MVx′,        MVy′) with the same rounding method as in the MV scaling        process.        -   a) Alternatively, the MV used in ATMVP to locate a            corresponding block in a different picture (e.g., the TMV            in 0) may be right-shifted to the integer precision with the            same rounding method as in the MV averaging process.        -   b) Alternatively, the MV used in ATMVP to locate a            corresponding block in a different picture (e.g., the TMV            in 0) may be right-shifted to the integer precision with the            same rounding method as in the adaptive MV resolution (AMVR)            process.    -   19. The MV(MVx, MVy) used in ATMVP to locate a corresponding        block in a different picture (e.g., the TMV in 0) may be        right-shifted to the integer precision (denoted as (MVx′, MVy′)        by rounding toward zero.        -   a) For example, MVx′=(MVx+((1<<N)>>1)−(MVx>=0? 1:0))>>N; N            is an integer presenting the MV resolution, e.g. N=4.            -   i. For example, MVx′=(MVx+(MVx>=0?7:8))>>4.        -   b) For example, MVy′=(MVy+((1<<N)>>1)−(MVy>=0?1:0))>>N; N is            an integer presenting the MV resolution, e.g. N=4.            -   i. For example, MVy′=(MVy+(MVy>=0?7:8))>>4.    -   20. In one example, MV(MVx, MVy) in bullet 18 and bullet 19 is        used to locate a corresponding block to derive the default        motion information used in ATMVP, such as using the center        position of the sub-block and the shifted MV, or using the        top-left position of current block and the shifted MV.        -   a) In one example, MV(MVx, MVy) is used to locate a            corresponding block to derive the motion information of a            sub-block in current block during the ATMVP process, such as            using the center position of the sub-block and the shifted            MV.    -   21. The proposed methods in bullet 18, 19, 20 may be also        applied to other coding tools that require to locate a reference        block in a different picture or current picture with a motion        vector.    -   22. The MV(MVx, MVy) used in ATMVP to locate a corresponding        block in a different picture (e.g., the TMV in 0) may be scaled        even it points to the collocated picture.        -   a) In one example, if the width and/or height of the            collocated picture (or the conformance window in it) is            different from that of the current picture (or the            conformance window in it), the MV may be scaled.        -   b) Suppose the width and height of (the conformance window)            of the collocated picture are denoted as W1 and H1,            respectively. The width and height of (the conformance            window of) the current picture are denoted as W2 and H2,            respectively. Then MV(MVx, MVy) may be scaled as            MVx′=MVx*W1/W2 and MVy′=MVy*H1/H2.    -   23. The center point of the current block (such as position (x0,        y0) in 2.3.5.1.2) used to derive motion information in the ATMVP        process may be further modified by scaling and/or adding        offsets.        -   a) In one example, if the width and/or height of the            collocated picture (or the conformance window in it) is            different from that of the current picture (or the            conformance window in it), the center point may be further            modified.        -   b) Suppose the top-left position of the conformance window            in the collocated picture are denoted as X1 and Y1. The            top-left position of the conformance window defined in the            current picture are denoted as X2 and Y2. The width and            height of (the conformance window of) the collocated picture            are denoted as W1 and H1, respectively. The width and height            of (the conformance window) of the current picture are            denoted as W2 and H2, respectively. Then (x0, y0) may be            modified as x0′=(x0−X2)*W1/W2+X1 and y0′=(y0−Y2)*H1/H2+Y1.            -   i. Alternatively, x0′=x0*W1/W2, y0′=y0*H1/H2.    -   24. The corresponding position (such as position M in 2.3.5.1.2)        used to derive motion information in the ATMVP process may be        further modified by scaling and/or adding offsets        -   a) In one example, if the width and/or height of the            collocated picture (or the conformance window in it) is            different from that of the current picture (or the            conformance window in it), the corresponding position may be            further modified.        -   b) Suppose the top-left position of the conformance window            in the collocated picture are denoted as X1 and Y1. The            top-left position of the conformance window defined in the            current picture are denoted as X2 and Y2. The width and            height of (the conformance window of) the collocated picture            are denoted as W1 and H1, respectively. The width and height            of (the conformance window) of the current picture are            denoted as W2 and H2, respectively. Then M(x, y) may be            modified as x′=(x−X2)*W1/W2+X1 and y′=(y−Y2)*H1/H2+Y1.            -   i. Alternatively, x′=x*W1/W2, y′=y*H1/H2.

Sub-Picture Related

-   -   25. In one example, the width of a sub-picture S ending at the        (j−1) column may be set equal to j minus the left-most column of        the sub-picture S, if the position (i, j) and (i, j−1) belong to        different sub-pictures.        -   a) An embodiment based on an existing implementation is            highlighted as below.

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) { for( j = 0; j< NumSubPicGridCols; j++ ) { if ( i = = 0) SubPicTop[ subpic_grid_idx[ i][ j ] ] = 0 else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i −1 ][ j ] ) { SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i SubPicHeight[subpic_grid_idx[ i − 1 ][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1][ j ] ] } if ( j = = 0) SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0(7-7) else if (subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1] ) { SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j SubPicWidth[ subpic_(—) grid _(—) idx[ i ][ j −1] ] = j − SubPicLeft[ subpic _(—) grid _(—)idx[ i ][ j − 1 ] ] } if ( i = = NumSubPicGridRows − 1) SubPicHeight[subpic_grid_idx[ i ][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j] ] + 1 if (j = = NumSubPicGridRows − 1) SubPicWidth[ subpic_grid_idx[ i][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ] + 1 if(subpic_grid_idx[ i ][ j ] > NumSubPics)  NumSubPics = subpic_grid_idx[ i][ j ] } }

-   -   26. In one example, the height of a sub-picture S ending at the        (NumSubPicGridRows−1) row may be set equal to        (NumSubPicGridRows−1) minus the top-most row of the sub-picture        S then plus one.        -   a) An embodiment based on an existing implementation is            highlighted as below.

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) { for( j = 0; j< NumSubPicGridCols; j++ ) { if ( i = = 0) SubPicTop[ subpic_grid_idx[ i][ j ] ] = 0 else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i −1 ][ j ] ) { SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i SubPicHeight[subpic_grid_idx[ i − 1][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1][ j ] ] } if ( j = = 0) SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0(7-7) else if (subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1] ) { SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j SubPicWidth[subpic_grid_idx[ i ][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j −1 ] ] } if ( i = = NumSubPicGridRows − 1) SubPicHeight[ subpic _(—) grid_(—) idx[ i ][ j ] ] = i − SubPicTop[ subpic _(—) grid _(—) idx[ i ][ j] ] + 1 if (j = = NumSubPicGridRows − 1) SubPicWidth[ subpic_grid_idx[ i][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ] + 1 if(subpic_grid_idx[ i ][ j ]] > NumSubPics) NumSubPics = subpic_grid_idx[ i][ j ]

-   -   27. In one example, the width of a sub-picture S ending at the        (NumSubPicGridColumns−1) column may be set equal to        (NumSubPicGridColumns−1) minus the left-most column of the        sub-picture S then plus 1.        -   a) An embodiment based on an existing implementation is            highlighted as below.

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) { for( j = 0; j< NumSubPicGridCols; j++ ) { if ( i = = 0) SubPicTop[ subpic_grid_idx[ i][ j ] ] = 0 else if( subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i −1 ][ j ] ) { SubPicTop[ subpic_grid_idx[ i ][ j ] ] = i SubPicHeight[subpic_grid_idx[ i − 1][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1][ j ] ] } if ( j = = 0) SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0(7-7) else if (subpic_grid_idx[ i ][ j ] ] != subpic_grid_idx[ i ][ j −1 ] ) { SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j SubPicWidth[subpic_grid_idx[ i ][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j −1 ] ] } if ( i = = NumSubPicGridRows − 1) SubPicHeight[ subpic_grid_idx[i ][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ] + 1 if (j == NumSubPicGridColumns − 1) SubPicWidth[ subpic _(—) grid _(—) idx[ i ][j ] ] = j − SubPicLeft[ subpic _(—) grid _(—) idx[ i ][ j ] ] + 1 if(subpic_grid_idx[ i ][ j ] > NumSubPics) NumSubPics = subpic_grid_idx[ i][ j ]

-   -   28. The sub-picture grid must be integer times of the CTU size.        -   a) An embodiment based on an existing implementation is            highlighted as below.            subpic_grid_col_width_minus1 plus 1 specifies the width of            each element of the subpicture identifier grid in units of            CtbSizeY. The length of the syntax element is Ceil(Log            2(pic_width_max_in_luma_samples/CtbSizeY)) bits.            The variable NumSubPicGridCols is derived as follows:

NumSubPicGridCols=(pic_width_max_in_luma_samples+subpic_grid_col_width_minus1*CtbSizeY+CtbSizeY−1)/(subpic_grid_col_width_minus1*CtbSizeY+CtbSizeY)  (7-5)

subpic_grid_row_height_minus1 plus 1 specifies the height of eachelement of the subpicture identifier grid in units of 4 samples. Thelength of the syntax element is Ceil(Log2(pic_height_max_in_luma_samples/CtbSizeY)) bits.The variable NumSubPicGridRows is derived as follows:

NumSubPicGridRows=(pic_height_max_in_luma_samples+subpic_grid_row_height_minus1*CtbSizeY+CtbSizeY−1)/(subpic_grid_row_height_minus1*CtbSizeY+CtbSizeY)  (7-6)

-   -   29. A conformance constrain is added to guarantee that        sub-pictures cannot be overlapped with each other, and all the        sub-pictures must cover the whole picture.        -   a) An embodiment based on an existing implementation is            highlighted as below            Any subpic_grid_idx[i][j] must be equal to idx if the            following conditions are both satisfied:

i>=SubPicTop[idx] and i<SubPicTop[idx]+SubPicHeight[idx].

j>=SubPicLeft[idx] and j<SubPicLeft[idx]+SubPicWidth[idx].

Any subpic_grid_idx[i][j] must be different to idx if the followingconditions are not both satisfied:

i>=SubPicTop[idx] and i<SubPicTop[idx]+SubPicHeight[idx].

j>=SubPicLeft[idx] and j<SubPicLeft[idx]+SubPicWidth[idx].

RPR related

-   -   30. A syntax element (such as a flag), denoted as RPR_flag, is        signaled to indicate whether RPR may be used or not in a video        unit (e.g., sequence). RPR_flag may be signaled in SPS, VPS, or        DPS.        -   a) In one example, if RPR is signaled not to be used (e.g.            RPR_flag is 0) all width/height signaled in PPS must be the            same to the maximum width/maximum height signaled in SPS.        -   b) In one example, if RPR is signaled not to be used (e.g.            RPR_flag is 0) all width/height in PPS is not signaled and            inferred to be the maximum width/maximum height signaled in            SPS.        -   c) In one example, if RPR is signaled not to be used (e.g.            RPR_flag is 0), conformance window information is not used            in the decoding process. Otherwise (RPR is signaled to be            used), conformance window information may be used in the            decoding process.    -   31. It is proposed that the interpolation filters used in the        motion compensation process to derive the prediction block of a        current block may be selected depending on whether the        resolution of the reference picture is different to the current        picture, or whether the width and/or height of the reference        picture is larger that of the current picture.        -   a. In one example, the interpolation filters with less taps            may be applied when condition A is satisfied, wherein            condition A depends on the dimensions of the current picture            and/or the reference picture.            -   i. In one example, condition A is the resolution of the                reference picture is different to the current picture.            -   ii. In one example, condition A is the width and/or                height of the reference picture is larger than that of                the current picture.            -   iii. In one example, condition A is W1>a*W2 and/or                H1>b*H2, wherein (W1, H1) represents the width and                height of the reference picture and (W2, H2) represents                the width and height of the current picture, a and b are                two factors, e.g. a=b=1.5.            -   iv. In one example, condition A may also depend on                whether bi-prediction is used.                -   1) Condition A is satisfied is satisfied only when                    bi-prediction is used for the current block.            -   v. In one example, condition A may depend on M and N,                where M and N represent the width and height of the                current block.                -   1) For example, condition A is satisfied only when                    M*N<=T, where T is an integer such as 64.                -   2) For example, condition A is satisfied only when                    M<=T1 or N<=T2, where T1 and T2 are integers, e.g.                    T1=T2=4.                -   3) For example, condition A is satisfied only when                    M<=T1 and N<=T2, where T1 and T2 are integers, e.g.                    T1=T2=4.                -   4) For example, condition A is satisfied only when                    M*N<=T, or M<=T1 or N<=T2, where T, T1 and T2 are                    integers, e.g. T=64, T1=T2=4.                -   5) In one example, the smaller condition in above                    sub-bullets may be replaced by greater.            -   vi. In one example, 1-tap filters are applied. In other                words, an integer pixel without filtering is output as                the interpolation result.            -   vii. In one example, bi-linear filters are applied when                the resolution of the reference picture is different to                the current picture.            -   viii. In one example, 4-tap filters or 6-tap filters are                applied when the resolution of the reference picture is                different to the current picture, or the width and/or                height of the reference picture is larger than that of                the current picture.                -   1) The 6-tap filters may also be used for the affine                    motion compensation.                -   2) The 4-tap filters may also be used for                    interpolation for chroma samples.        -   b. Whether to and/or how to apply the methods disclosed in            bullet 31 may depend on the color components.            -   i. For example, the methods are only applied on the luma                component.        -   c. Whether to and/or how to apply the methods disclosed in            bullet 31 may depend on the interpolation filtering            direction.            -   i. For example, the methods are only applied on                horizontal filtering.            -   ii. For example, the methods are only applied on                vertical filtering.                CIIP related    -   32. Intra prediction signal used in CIP process may be done in        TU level instead of CU level (e.g., using reference samples        outside the TU instead of CU).        -   a) In one example, if either CU width or height is greater            than the max transform block size, the CU may be split to            multiple TUs and intra/inter prediction may be generated for            each TU, e.g., using reference samples outside the TU.        -   b) In one example, if the maximum transform size K is            smaller than 64 (such as K=32), then the intra-prediction            used in CIIP is performed in a recursive way like in a            normal intra-code block.        -   c) For example, a KM×KN CIIP coded block where M and N are            integers are split into MN of K×K blocks, Intra-prediction            is done for each K×K block. The intra-prediction for a later            coded/decoded K×K block may depend on the reconstruction            samples of a previously coded/decoded K×K block.

5. Additional Example Embodiments (Boldfaced Shows Changes Made to theCurrent Version of the Standard) 5.1 Embodiment #1: An Example of SyntaxDesign in SPS/PPS/Slice Header/Tile Group Header

The changes compared to the VTM3.0.1rc1 reference software ishighlighted in large size bold face font as follow:

if( sps_temporal_mvp_enabled_flag )  slice _(—) temporal _(—) mvp _(—)enabled _(—) flag u(1) if( slice_type = = B )  mvd _(—) l1 _(—) zero_(—) flag u(1) if( slice_temporal_mvp_enabled_flag ) {  if( slice_type == B )  collocated _(—) from _(—) l0 _(—) flag u(1) } ... if(!sps_affine_enabled_flag) {  if(!(sps_sbtmvp_enabled_flag && slice_(—) temporal _(—) mvp _(—) enabled _(—) flag ))MaxSubBlockMergeListSize = 0 else MaxSubBlockMergeListSize = 1  }  else{ five _(—) minus _(—) max _(—) num _(—) affine _(—) merge _(—) candue(v)  MaxSubBlockMergeListSize = 5-five_minus_max_num_affine_merge_cand  }

5.2 Embodiment #2: An Example of Syntax Design in SPS/PPS/SliceHeader/Tile Group Header 7.3.2.1 Sequence Parameter Set RBSP Syntax

Descriptor seq_parameter_set_rbsp( ) { sps _(—) seq _(—) parameter _(—)set _(—) id ue(v) chroma _(—) format _(—) idc ue(v) ... sps _(—) ref_(—) wraparound _(—) enabled _(—) flag u(1) if(sps_ref_wraparound_enabled_flag ) sps _(—) ref _(—) wraparound _(—)offset ue(v) sps _(—) temporal _(—) mvp _(—) enabled _(—) flag u(1) if(sps_temporal_mvp_enabled_flag ) sps _(—) sbtmvp _(—) enabled _(—) flagu(1) sps _(—) amvr _(—) enabled _(—) flag u(1) ... } rbsp_trailing_bits() }

sps_sbtmvpsenabledtflag equal to 1 specifies that subblock-basedtemporal motion vector predictors may be used in decoding of pictureswith all slices having slice_type not equal to I in the CVS.sps_sbtmvp_enabledjflag equal to 0 specifies that subblock-basedtemporal motion vector predictors are not used in the CVS. Whensps_sbtmvp_enabled_flag is not present, it is inferred to be equal to 0.

five_minus_max_num_subblock_merge_cand specifies the maximum number ofsubblock-based merging motion vector prediction (MVP) candidatessupported in the slice subtracted from 5. Whenfive_minus_max_num_subblocktmerge_cand is not present, it is inferred tobe equal to 5−sps_sbtmvpsenabledtflag. The maximum number ofsubblock-based merging MVP candidates, MaxNumSubblockMergeC and isderived as follows:

MaxNumSubblockMergeCand=5−five_minus_max_num_subblock_merge_cand(7-45)

The value of MaxNumSubblockMergeCand shall be in the range of 0 to 5,inclusive.

8.3.4.2 Derivation Process for Motion Vectors and Reference Indices inSubblock Merge Mode

Inputs to this Process are:

. . . [No changes to the current VVC specification draft].

Outputs of this Process are:

. . . [No changes to the current VVC specification draft].

The variables numSbX, numSbY and the subblock merging candidate list,subblockMergeCandList are derived by the following ordered steps:

When sps_sbtmvp_enabled_flag is equal to 1 and (current picture is anIRAP and index 0 of reference picture list 0 is the current picture) isnot true, the following applies:

The derivation process for merging candidates from neighbouring codingunits as specified in clause 8.3.2.3 is invoked with the luma codingblock location (xCb, yCb), the luma coding block width cbWidth, the lumacoding block height cbHeight and the luma coding block width as inputs,and the output being the availability flags availableFlagA0,availableFlagA1, availableFlagB0, availableFlagB1 and availableFlagB2,the reference indices refIdxLXA0, refIdxLXA1, refIdxLXB0, refIdxLXB1 andrefIdxLXB2, the prediction list utilization flags predFlagLXA0,predFlagLXA1, predFlagLXB0, predFlagLXB1 and predFlagLXB2, and themotion vectors mvLXA0, mvLXA1, mvLXB0, mvLXB1 and mvLXB2, with X being 0or 1.

The derivation process for subblock-based temporal merging candidates asspecified in clause 8.3.4.3 is invoked with the luma location (xCb,yCb), the luma coding block width cbWidth, the luma coding block heightcbHeight, the availability flags availableFlagA0, availableFlagA1,availableFlagB0, availableFlagB1, the reference indices refIdxLXA0,refIdxLXA1, refIdxLXB0, refIdxLXB1, the prediction list utilizationflags predFlagLXA0, predFlagLXA1, predFlagLXB0, predFlagLXB1 and themotion vectors mvLXA0, mvLXA1, mvLXB0, mvLXB1 as inputs and the outputbeing the availability flag availableFlagSbCol, the number of lumacoding subblocks in horizontal direction numSbX and in verticaldirection numSbY, the reference indices refIdxLXSbCol, the luma motionvectors mvLXSbCol[xSbIdx][ySbIdx] and the prediction list utilizationflags predFlagLXSbCol[xSbIdx][ySbIdx] with xSbIdx=0 . . . numSbX−1,ySbIdx=0 . . . numSbY−1 and X being 0 or 1.

When sps_affine_enabled_flag is equal to 1, the sample locations (xNbA0,yNbA0), (xNbA1, yNbA1), (xNbA2, yNbA2), (xNbB0, yNbB0), (xNbB1, yNbB1),(xNbB2, yNbB2), (xNbB3, yNbB3), and the variables numSbX and numSbY arederived as follows:

[No changes to the current VVC specification draft].

5.3 Embodiment #3 an Example of MV Rounding

The syntax changes are based on an existing implementation.

8.5.5.3 Derivation Process for Subblock-Based Temporal MergingCandidates

. . . .

-   -   The location (xColSb, yColSb) of the collocated subblock inside        ColPic is derived as follows.        -   1. The following applies:

yColSb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),ySb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   -   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1,                the following applies:

xColSb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xSb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   -   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is                equal to 0), the following applies:

xColSb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xSb+(tempMv[0]+8+(tempMV[0]>=0))>>4))

. . . .

8.5.5.4 Derivation Process for Subblock-Based Temporal Merging BaseMotion Data

. . . .The location (xColCb, yColCb) of the collocated block inside ColPic isderived as follows.

-   -   The following applies:

yColCb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),yColCtrCb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0,        the following applies:

xColCb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

5.3 Embodiment #3: An Example of MV Rounding

The syntax changes are based on an existing implementation.

8.5.5.3 Derivation Process for Subblock-Based Temporal MergingCandidates

. . . .

-   -   The location (xColSb, yColSb) of the collocated subblock inside        ColPic is derived as follows.    -   1. The following applies:

yColSb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),ySb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the            following applies:

xColSb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xSb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to            0), the following applies:

xColSb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xSb+(tempMv[0]+8+(tempMV[0]>=0))>>4))

. . . .

8.5.5.4 Derivation Process for Subblock-Based Temporal Merging BaseMotion Data

. . . .The location (xColCb, yColCb) of the collocated block inside ColPic isderived as follows.

-   -   The following applies:

yColCb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),yColCtrCb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0,        the following applies:

xColCb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

5.4 Embodiment #4: A Second Example of MV Rounding 8.5.5.3 DerivationProcess for Subblock-Based Temporal Merging Candidates

Inputs to this Process are:

-   -   a luma location (xCb, yCb) of the top-left sample of the current        luma coding block relative to the top-left luma sample of the        current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.    -   the availability flag availableFlagA1 of the neighbouring coding        unit,    -   the reference index refIdxLXA₁ of the neighbouring coding unit        with X being 0 or 1,    -   the prediction list utilization flag predFlagLXA₁ of the        neighbouring coding unit with X being 0 or 1,    -   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of        the neighbouring coding unit with X being 0 or 1.        Outputs of this Process are:    -   the availability flag availableFlagSbCol,    -   the number of luma coding subblocks in horizontal direction        numSbX and in vertical direction numSbY,    -   the reference indices refIdxL0SbCol and refIdxL1SbCol,    -   the luma motion vectors in 1/16 fractional-sample accuracy        mvL0SbCol[xSbIdx][ySbIdx] and mvL1SbCol[xSbIdx][ySbIdx] with        xSbIdx=0 . . . numSbX−1, ySbIdx=0 . . . numSbY−1,    -   the prediction list utilization flags        predFlagL0SbCol[xSbIdx][ySbIdx] and        predFlagL1SbCol[xSbIdx][ySbIdx] with xSbIdx=0 . . . numSbX−1,        ySbIdx=0 . . . numSbY−1.

The availability flag availableFlagSbCol is derived as follows.

-   -   If one or more of the following conditions is true,        availableFlagSbCol is set equal to 0.    -   slice_temporal_mvp_enabled_flag is equal to 0.    -   sps_sbtmvp_enabled_flag is equal to 0.    -   cbWidth is less than 8.    -   cbHeight is less than 8.    -   Otherwise, the following ordered steps apply:        -   1. The location (xCtb, yCtb) of the top-left sample of the            luma coding tree block that contains the current coding            block and the location (xCtr, yCtr) of the below-right            center sample of the current luma coding block are derived            as follows:

xCtb=(xCb>>CtuLog2Size)<<CtuLog2Size  (8-542)

yCtb=(yCb>>CtuLog2Size)<<CtuLog2Size  (8-543)

xCtr=xCb+(cbWidth/2)  (8-544)

yCtr=yCb+(cbHeight/2)  (8-545)

-   -   -   2. The luma location (xColCtrCb, yColCtrCb) is set equal to            the top-left sample of the collocated luma coding block            covering the location given by (xCtr, yCtr) inside ColPic            relative to the top-left luma sample of the collocated            picture specified by ColPic.        -   3. The derivation process for subblock-based temporal            merging base motion data as specified in clause 8.5.5.4 is            invoked with the location (xCtb, yCtb), the location            (xColCtrCb, yColCtrCb), the availability flag            availableFlagA₁, and the prediction list utilization flag            predFlagLXA₁, and the reference index refIdxLXA₁, and the            motion vector mvLXA₁, with X being 0 and 1 as inputs and the            motion vectors ctrMvLX, and the prediction list utilization            flags ctrPredFlagLX of the collocated block, with X being 0            and 1, and the temporal motion vector tempMv as outputs.        -   4. The variable availableFlagSbCol is derived as follows:            -   If both ctrPredFlagL0 and ctrPredFlagL1 are equal to 0,                availableFlagSbCol is set equal to 0.            -   Otherwise, availableFlagSbCol is set equal to 1.                When availableFlagSbCol is equal to 1, the following                applies:

    -   The variables numSbX, numSbY, sbWidth, sbHeight and        refIdxLXSbCol are derived as follows:

numSbX=cbWidth>>3   (8-546)

numSbY=cbHeight>>3   (8-547)

sbWidth=cbWidth/numSbX   (8-548)

sbHeight=cbHeight/numSbY   (8-549)

refIdxLXSbCol=0   (8-550)

-   -   For xSbIdx=0 . . . numSbX−1 and ySbIdx=0 . . . numSbY−1, the        motion vectors mvLXSbCol[xSbIdx][ySbIdx] and prediction list        utilization flags predFlagLXSbCol[xSbIdx][ySbIdx] are derived as        follows:        -   The luma location (xSb, ySb) specifying the top-left sample            of the current coding subblock relative to the top-left luma            sample of the current picture is derived as follows:

xSb=xCb+xSbIdx*sbWidth+sbWidth/2  (8-551)

ySb=yCb+ySbIdx*sbHeight+sbHeight/2  (8-552)

-   -   The location (xColSb, yColSb) of the collocated subblock inside        ColPic is derived as follows.        -   1. The following applies:

yColSb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),ySb+((tempMv[1]+8−(tempMv[1]>=0?1:0))>>4))  (8−553)

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColSb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xSb+((tempMv[0]+8−(tempMv[0]>=0?1:0))>>4))  (8−554)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),        the following applies:

xColSb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xSb+((tempMv[0]+8−(tempMv[0]>=0?1:0))>>4))  (8−555)

-   -   The variable currCb specifies the luma coding block covering the        current coding subblock inside the current picture.    -   The variable colCb specifies the luma coding block covering the        modified location given by ((xColSb>>3)<<3, (yColSb>>3)<<3)        inside the ColPic.    -   The luma location (xColCb, yColCb) is set equal to the top-left        sample of the collocated luma coding block specified by colCb        relative to the top-left luma sample of the collocated picture        specified by ColPic.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL0 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL0SbCol[xSbIdx][ySbIdx] and        availableFlagL0SbCol.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL1 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL1SbCol[xSbIdx][ySbIdx] and        availableFlagL1SbCol.    -   When availableFlagL0SbCol and availableFlagL1SbCol are both        equal to 0, the following applies for X being 0 and 1:

mvLXSbCol[xSbIdx][ySbIdx]=ctrMvLX   (8-556)

predFlagLXSbCol[xSbIdx][ySbIdx]=ctrPredFlagLX  (8-557)

8.5.5.4 Derivation process for subblock-based temporal merging basemotion data Inputs to this process are:

-   -   the location (xCtb, yCtb) of the top-left sample of the luma        coding tree block that contains the current coding block,    -   the location (xColCtrCb, yColCtrCb) of the top-left sample of        the collocated luma coding block that covers the below-right        center sample.    -   the availability flag availableFlagA1 of the neighbouring coding        unit,    -   the reference index refIdxLXA₁ of the neighbouring coding unit,    -   the prediction list utilization flag predFlagLXA1 of the        neighbouring coding unit,    -   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of        the neighbouring coding unit.

Outputs of this process are:

-   -   the motion vectors ctrMvL0 and ctrMvL1,    -   the prediction list utilization flags ctrPredFlagL0 and        ctrPredFlagL1,    -   the temporal motion vector tempMv.

The variable tempMv is set as follows:

tempMv[0]=0  (8-558)

tempMv[1]=0  (8-559)

The variable currPic specifies the current picture.When availableFlagA1 is equal to TRUE, the following applies:

-   -   If all of the following conditions are true, tempMv is set equal        to mvL0A₁:        -   predFlagL0A1 is equal to 1,        -   DiffPicOrderCnt(ColPic, RefPicList[0][refIdxL0A1]) is equal            to 0,    -   Otherwise, if all of the following conditions are true, tempMv        is set equal to mvL1A₁:        -   slice_type is equal to B,        -   predFlagL1A₁ is equal to 1,        -   DiffPicOrderCnt(ColPic, RefPicList[1][refIdxL1A₁]) is equal            to 0.            The location (xColCb, yColCb) of the collocated block inside            ColPic is derived as follows.    -   The following applies:

yColCb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),yColCtrCb+((tempMv[1]+8−(tempMv[1]>=0?1:0))>>4))  (8-560)

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+8−(tempMv[0]>=0?1:0))>>4))  (8-561)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to o,        the following applies:

xColCb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+8−(tempMv[0]>=0?1:0))>>4))  (8-562)

The array colPredMode is set equal to the prediction mode arrayCuPredMode[0] of the collocated picture specified by ColPic.

The motion vectors ctrMvL0 and ctrMvL1, and the prediction listutilization flags ctrPredFlagL0 and ctrPredFlagL1 are derived asfollows:

-   -   If colPredMode[xColCb][yColCb] is equal to MODE_INTER, the        following applies:        -   The variable currCb specifies the luma coding block covering            (xCtrCb,yCtrCb) inside the current picture.        -   The variable colCb specifies the luma coding block covering            the modified location given by ((xColCb>>3)<<3,            (yColCb>>3)<<3) inside the ColPic.        -   The luma location (xColCb, yColCb) is set equal to the            top-left sample of the collocated luma coding block            specified by colCb relative to the top-left luma sample of            the collocated picture specified by ColPic.        -   The derivation process for collocated motion vectors            specified in clause 8.5.2.12 is invoked with currCb, colCb,            (xColCb, yColCb), refIdxL0 set equal to 0, and sbFlag set            equal to 1 as inputs and the output being assigned to            ctrMvL0 and ctrPredFlagL0.        -   The derivation process for collocated motion vectors            specified in clause 8.5.2.12 is invoked with currCb, colCb,            (xColCb, yColCb), refIdxL1 set equal to 0, and sbFlag set            equal to 1 as inputs and the output being assigned to            ctrMvL1 and ctrPredFlagL1.    -   Otherwise, the following applies:

ctrPredFlagL0=0  (8-563)

ctrPredFlagL1=0  (8-564)

5.5 Embodiment #5: A Third Example of MV Rounding 8.5.5.3 DerivationProcess for Subblock-Based Temporal Merging Candidates

Inputs to this Process are:

-   -   a luma location (xCb, yCb) of the top-left sample of the current        luma coding block relative to the top-left luma sample of the        current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.    -   the availability flag availableFlagA₁ of the neighbouring coding        unit,    -   the reference index refIdxLXA1 of the neighbouring coding unit        with X being 0 or 1,    -   the prediction list utilization flag predFlagLXA₁ of the        neighbouring coding unit with X being 0 or 1,    -   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of        the neighbouring coding unit with X being 0 or 1.        Outputs of this Process are:    -   the availability flag availableFlagSbCol,    -   the number of luma coding subblocks in horizontal direction        numSbX and in vertical direction numSbY,    -   the reference indices refIdxL0SbCol and refIdxL1SbCol,    -   the luma motion vectors in 1/16 fractional-sample accuracy        mvL0SbCol[xSbIdx][ySbIdx] and mvL1SbCol[xSbIdx][ySbIdx] with        xSbIdx=0 . . . numSbX−1, ySbIdx=0 . . . numSbY−1,    -   the prediction list utilization flags        predFlagL0SbCol[xSbIdx][ySbIdx] and        predFlagL1SbCol[xSbIdx][ySbIdx] with xSbIdx=0 . . . numSbX−1,        ySbIdx=0 . . . numSbY−1.        The availability flag availableFlagSbCol is derived as follows.    -   If one or more of the following conditions is true,        availableFlagSbCol is set equal to 0.    -   slice_temporal_mvp_enabled_flag is equal to 0.    -   sps_sbtmvp_enabled_flag is equal to 0.    -   cbWidth is less than 8.    -   cbHeight is less than 8.    -   Otherwise, the following ordered steps apply:        -   5. The location (xCtb, yCtb) of the top-left sample of the            luma coding tree block that contains the current coding            block and the location (xCtr, yCtr) of the below-right            center sample of the current luma coding block are derived            as follows:

xCtb=(xCb>>CtuLog2Size)<<CtuLog2Size  (8-542)

yCtb=(yCb>>CtuLog2Size)<<CtuLog2Size  (8-543)

xCtr=xCb+(cbWidth/2)  (8-544)

yCtr=yCb+(cbHeight/2)  (8-545)

-   -   -   6. The luma location (xColCtrCb, yColCtrCb) is set equal to            the top-left sample of the collocated luma coding block            covering the location given by (xCtr, yCtr) inside ColPic            relative to the top-left luma sample of the collocated            picture specified by ColPic.        -   7. The derivation process for subblock-based temporal            merging base motion data as specified in clause 8.5.5.4 is            invoked with the location (xCtb, yCtb), the location            (xColCtrCb, yColCtrCb), the availability flag            availableFlagA1, and the prediction list utilization flag            predFlagLXA1, and the reference index refIdxLXA₁, and the            motion vector mvLXA₁, with X being 0 and 1 as inputs and the            motion vectors ctrMvLX, and the prediction list utilization            flags ctrPredFlagLX of the collocated block, with X being 0            and 1, and the temporal motion vector tempMv as outputs.        -   8. The variable availableFlagSbCol is derived as follows:            -   If both ctrPredFlagL0 and ctrPredFlagL1 are equal to 0,                availableFlagSbCol is set equal to 0.            -   Otherwise, availableFlagSbCol is set equal to 1.                When availableFlagSbCol is equal to 1, the following                applies:

    -   The variables numSbX, numSbY, sbWidth, sbHeight and        refIdxLXSbCol are derived as follows:

numSbX=cbWidth>>3   (8-546)

numSbY=cbHeight>>3   (8-547)

sbWidth=cbWidth/numSbX   (8-548)

sbHeight=cbHeight/numSbY   (8-549)

refIdxLXSbCol=0   (8-550)

-   -   For xSbIdx=0 . . . numSbX−1 and ySbIdx=0 . . . numSbY−1, the        motion vectors mvLXSbCol[xSbIdx][ySbIdx] and prediction list        utilization flags predFlagLXSbCol[xSbIdx][ySbIdx] are derived as        follows:        -   The luma location (xSb, ySb) specifying the top-left sample            of the current coding subblock relative to the top-left luma            sample of the current picture is derived as follows:

xSb=xCb+xSbIdx*sbWidth+sbWidth/2  (8-551)

ySb=yCb+ySbIdx*sbHeight+sbHeight/2  (8-552)

-   -   The location (xColSb, yColSb) of the collocated subblock inside        ColPic is derived as follows.        -   1. The following applies:

yColSb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),ySb+((tempMv[1]+(tempMv[1]>=0?7:8))>>4))  (8-553)

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColSb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xSb+((tempMv[0]+(tempMv[0]>=0?7:8))>>4))  (8-554)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),        the following applies:

xColSb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xSb+((tempMv[0]+(tempMv[0]>=0?7:8))>>4))  (8-555)

-   -   The variable currCb specifies the luma coding block covering the        current coding subblock inside the current picture.    -   The variable colCb specifies the luma coding block covering the        modified location given by ((xColSb>>3)<<3, (yColSb>>3)<<3)        inside the ColPic.    -   The luma location (xColCb, yColCb) is set equal to the top-left        sample of the collocated luma coding block specified by colCb        relative to the top-left luma sample of the collocated picture        specified by ColPic.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL0 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL0SbCol[xSbIdx][ySbIdx] and        availableFlagL0SbCol.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL1 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL1SbCol[xSbIdx][ySbIdx] and        availableFlagL1SbCol.    -   When availableFlagL0SbCol and availableFlagL1SbCol are both        equal to 0, the following applies for X being 0 and 1:

mvLXSbCol[xSbIdx][ySbIdx]=ctrMvLX   (8-556)

predFlagLXSbCol[xSbIdx][ySbIdx]=ctrPredFlagLX  (8-557)

8.5.5.4 Derivation Process for Subblock-Based Temporal Merging BaseMotion Data

Inputs to this Process are:

-   -   the location (xCtb, yCtb) of the top-left sample of the luma        coding tree block that contains the current coding block,    -   the location (xColCtrCb, yColCtrCb) of the top-left sample of        the collocated luma coding block that covers the below-right        center sample.    -   the availability flag availableFlagA1 of the neighbouring coding        unit,    -   the reference index refIdxLXA₁ of the neighbouring coding unit,    -   the prediction list utilization flag predFlagLXA1 of the        neighbouring coding unit,    -   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of        the neighbouring coding unit.        Outputs of this Process are:    -   the motion vectors ctrMvL0 and ctrMvL1,    -   the prediction list utilization flags ctrPredFlagL0 and        ctrPredFlagL1,    -   the temporal motion vector tempMv.

The variable tempMv is set as follows:

tempMv[0]=0  (8-558)

tempMv[1]=0  (8-559)

The variable currPic specifies the current picture.When availableFlagA1 is equal to TRUE, the following applies:

-   -   If all of the following conditions are true, tempMv is set equal        to mvL0A₁:        -   predFlagL0A₁ is equal to 1,        -   DiffPicOrderCnt(ColPic, RefPicList[0][refIdxL0A₁]) is equal            to 0,    -   Otherwise, if all of the following conditions are true, tempMv        is set equal to mvL1A₁:        -   slice_type is equal to B,    -   predFlagL1A₁ is equal to 1,    -   DiffPicOrderCnt(ColPic, RefPicList[1][refIdxL1A₁]) is equal to        0.        The location (xColCb, yColCb) of the collocated block inside        ColPic is derived as follows.    -   The following applies:

yColCb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1,yCtb+(1<<CtbLog2SizeY)−1),yColCtrCb+((tempMv[1]+(tempMv[1]>=0?7:8))>>4))  (8-560)

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb,Min(SubPicRightBoundaryPos,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+(tempMv[0]>=0?7:8))>>4))  (8-561)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to o,        the following applies:

xColCb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1,xCtb+(1<<CtbLog2SizeY)+3),xColCtrCb+((tempMv[0]+(tempMv[0]>=0?7:8))>>4))  (8-562)

The array colPredMode is set equal to the prediction mode arrayCuPredMode[0] of the collocated picture specified by ColPic.The motion vectors ctrMvL0 and ctrMvL1, and the prediction listutilization flags ctrPredFlagL0 and ctrPredFlagL1 are derived asfollows:

-   -   If colPredMode[xColCb][yColCb] is equal to MODE_INTER, the        following applies:        -   The variable currCb specifies the luma coding block covering            (xCtrCb,yCtrCb) inside the current picture.        -   The variable colCb specifies the luma coding block covering            the modified location given by ((xColCb>>3)<<3,            (yColCb>>3)<<3) inside the ColPic.        -   The luma location (xColCb, yColCb) is set equal to the            top-left sample of the collocated luma coding block            specified by colCb relative to the top-left luma sample of            the collocated picture specified by ColPic.        -   The derivation process for collocated motion vectors            specified in clause 8.5.2.12 is invoked with currCb, colCb,            (xColCb, yColCb), refIdxL0 set equal to 0, and sbFlag set            equal to 1 as inputs and the output being assigned to            ctrMvL0 and ctrPredFlagL0.        -   The derivation process for collocated motion vectors            specified in clause 8.5.2.12 is invoked with currCb, colCb,            (xColCb, yColCb), refIdxL1 set equal to 0, and sbFlag set            equal to 1 as inputs and the output being assigned to            ctrMvL1 and ctrPredFlagL1.    -   Otherwise, the following applies:

ctrPredFlagL0=0  (8-563)

ctrPredFlagL1=0  (8-564)

8.5.6.3 Fractional Sample Interpolation Process 8.5.6.3.1 General

Inputs to this Process are:

-   -   a luma location (xSb, ySb) specifying the top-left sample of the        current coding subblock relative to the top-left luma sample of        the current picture,    -   a variable sbWidth specifying the width of the current coding        subblock,    -   a variable sbHeight specifying the height of the current coding        subblock,    -   a motion vector offset mvOffset,    -   a refined motion vector refMvLX,    -   the selected reference picture sample array refPicLX,    -   the half sample interpolation filter index hpelIfIdx,    -   the bi-directional optical flow flag bdofFlag,    -   a variable cIdx specifying the colour component index of the        current block.        Outputs of this Process are:    -   an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array        predSamplesLX of prediction sample values.        The prediction block border extension size brdExtSize is derived        as follows:

brdExtSize=(bdofFlag∥(inter_affine_flag[xSb][ySb]&&sps_affine_prof_enabled_flag))?2:0  (8-752)

The variable fRefWidth is set equal to the PicOutputWidthL of thereference picture in luma samples.The variable fRefHeight is set equal to PicOutputHeightL of thereference picture in luma samples.The motion vector mvLX is set equal to (refMvLX−mvOffset).

-   -   If cIdx is equal to 0, the following applies:        -   The scaling factors and their fixed-point representations            are defined as

hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)

vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)

-   -   -   Let (xIntL, yIntL) be a luma location given in full-sample            units and (xFracL, yFracL) be an offset given in 1/16-sample            units. These variables are used only in this clause for            specifying fractional-sample locations inside the reference            sample arrays refPicLX.        -   The top-left coordinate of the bounding block for reference            sample padding (xSbInt_(L), ySbInt_(L)) is set equal to            (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).        -   For each luma sample location (x_(L)=0 . . .            sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)            inside the prediction luma sample array predSamplesLX, the            corresponding prediction luma sample value            predSamplesLX[x_(L)][y_(L)] is derived as follows:        -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be            luma locations pointed to by a motion vector (refMvLX[0],            refMvLX[1]) given in 1/16-sample units. The variables            refxSb_(L), refx_(L), refySb_(L), and refy_(L) are derived            as follows:

refxSb _(L)=((xSb<<4)+refMvLX[0])*hori_scale_fp  (8-755)

refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x_(L)*((hori_scale_fp+8)>>4))+32)>>6  (8-756)

refySb _(L)=((ySb>>4)+refMvLX[1])*vert_scale_fp  (8-757)

refyL=((Sign(refySb)*((Abs(refySb)+128)>>8)+yL*((vert_scale_fp+8)>>4))+32)>>6  (8-758)

-   -   -   The variables xInt_(L), yInt_(L), xFrac_(L) and yFrac_(L)            are derived as follows:

xInt _(L) =refx _(L)>>4   (8-759)

yInt _(L) =refy _(L)>>4   (8-760)

xFrac _(L) =refx _(L) & 15   (8-761)

yFrac _(L) =refy _(L) & 15   (8-762)

-   -   -   using6TapFlag is set to be 1 if all the conditions below are            satisfied:

cbWidth[0][xSb][ySb]<=4∥cbHeight[0][xSb][ySb]<=4∥cbWidth[0][xSb][ySb]*cbHeight[0][xSb][ySb]<=64.

PredFlagL0[xSb][ySb]==1 && PredFlagL1[xSb][ySb]==1.

-   -   -   If bdofFlag is equal to TRUE or            (sps_affine_prof_enabled_flag is equal to TRUE and            inter_affine_flag[xSb][ySb] is equal to TRUE), and one or            more of the following conditions are true, the prediction            luma sample value predSamplesLX[x_(L)][y_(L)] is derived by            invoking the luma integer sample fetching process as            specified in clause 8.5.6.3.3 with            (xInt_(L)+(xFrac_(L)>>3)−1), yInt_(L)+(yFrac_(L)>>3)−1) and            refPicLX as inputs.        -   1. x_(L) is equal to 0.        -   2. x_(L) is equal to sbWidth+1.        -   3. y_(L) is equal to 0.        -   4. y_(L) is equal to sbHeight+1.        -   Otherwise, the prediction luma sample value            predSamplesLX[xL][yL] is derived by invoking the luma sample            8-tap interpolation filtering process as specified in clause            8.5.6.3.2 with (xInt_(L)−(brdExtSize>0?1:0),            yIntL−(brdExtSize>0?1:0)), (xFracL, yFracL), (xSbInt_(L),            ySbint_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and            (xSb, ySb) and using6TapFlag as inputs.

    -   Otherwise (cIdx is not equal to 0), the following applies:        -   Let (xInt_(C), yInt_(C)) be a chroma location given in            full-sample units and (xFrac_(C), yFrac_(C)) be an offset            given in 1/32 sample units. These variables are used only in            this clause for specifying general fractional-sample            locations inside the reference sample arrays refPicLX.        -   The top-left coordinate of the bounding block for reference            sample padding (xSbIntC, ySbIntC) is set equal to            ((xSb/SubWidthC)+(mvLX[0]>>5),            (ySb/SubHeightC)+(mvLX[1]>>5)).        -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0            . . . sbHeight−1) inside the prediction chroma sample arrays            predSamplesLX, the corresponding prediction chroma sample            value predSamplesLX[xC][yC] is derived as follows:        -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be            chroma locations pointed to by a motion vector (mvLX[0],            mvLX[1]) given in 1/32-sample units. The variables            refxSb_(C), refySb_(C), refx_(C) and refy_(C) are derived as            follows:

refxSb _(C)=((xSb/SubWidthC<<5)+mvLX[0])*hori_scale_fp  (8-763)

refx _(C)=((Sign(refxSb _(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5  (8-764)

refySb _(C)=((ySb/SubHeightC>>5)+mvLX[1])*vert_scale_fp  (8-765)

refy _(C)=((Sign(refySb _(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5  (8-766)

-   -   -   The variables xInt_(C), yInt_(C), xFrac_(C) and yFrac_(C)            are derived as follows:

xInt _(C) =refx _(C)>>5   (8-767)

yInt _(C) =refy _(C)>>5   (8-768)

xFrac _(C) =refy _(C) & 31   (8-769)

yFrac _(C) =refy _(C) & 31   (8-770)

-   -   The prediction sample value predSamplesLX[xC][yC] is derived by        invoking the process specified in clause 8.5.6.3.4 with        (xInt_(C), yInt_(C)), (xFrac_(C), yFrac_(C)), (xSbIntC,        ySbIntC), sbWidth, sbHeight and refPicLX as inputs.

8.5.6.3.2 Luma Sample Interpolation Filtering Process

Inputs to this Process are:

-   -   a luma location in full-sample units (xInt_(L), yInt_(L)),    -   a luma location in fractional-sample units (xFrac_(L),        yFrac_(L)),    -   a luma location in full-sample units (xSbInt_(L), ySbInt_(L))        specifying the top-left sample of the bounding block for        reference sample padding relative to the top-left luma sample of        the reference picture,    -   the luma reference sample array refPicLx_(L),    -   the half sample interpolation filter index hpelIfIdx,    -   a variable sbWidth specifying the width of the current subblock,    -   a variable sbHeight specifying the height of the current        subblock,    -   a luma location (xSb, ySb) specifying the top-left sample of the        current subblock relative to the top-left luma sample of the        current picture,    -   a flag using6TapFlag specifying whether the 6-tap interpolation        filter used.        Output of this process is a predicted luma sample value        predSampleLx_(L)        The variables shift1, shift2 and shift3 are derived as follows:    -   The variable shift1 is set equal to Min(4, BitDepth_(Y)−8), the        variable shift2 is set equal to 6 and the variable shift3 is set        equal to Max(2, 14−BitDepth_(Y)).    -   The variable picW is set equal to pic_width_in_luma_samples and        the variable picH is set equal to pic_height_in_luma_samples.        The luma interpolation filter coefficients f_(L)[p] for each        1/16 fractional sample position p equal to xFrac_(L) or        yFrac_(L) are derived as follows:    -   If at least one of the following conditions are satisfied, the        luma interpolation filter coefficients f_(L)[p] are specified in        Table 8-12.        -   MotionModelIdc[xSb][ySb] is greater than 0, and sbWidth and            sbHeight are both equal to 4,        -   using6TapFlag is equal to 1.    -   Otherwise, the luma interpolation filter coefficients f_(L)[p]        are specified in Table 8-11 depending on hpelIfIdx.        The luma locations in full-sample units (xInt_(i), yInt_(i)) are        derived as follows for i=0 . . . 7:    -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xInt _(i)=Clip3(SubPicLeftBoundaryPos,SubPicRightBoundaryPos,xInt _(L)+i−3)  (8-771)

yInt _(i)=Clip3(SubPicTopBoundaryPos,SubPicBotBoundaryPos,yInt _(L)+i−3)  (8-772)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),        the following applies:

xInt_(i)=Clip3(0,picW−1,sps_ref_wraparound_enabled_flag?ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY,picW,xInt_(L) +i−3):xInt _(L) +i−3)   (8-773)

yInt _(i)=Clip3(0,picH−1,yInt _(L) +i−3)   (8-774)

The luma locations in full-sample units are further modified as followsfor i=0 . . . 7:

xInt _(i)=Clip3(xSbInt _(L)−3,xSbInt _(L)+sbWidth+4,xInt _(i))  (8-775)

yInt _(i)=Clip3(ySbInt _(L)−3,ySbInt _(L)+sbHeight+4,yInt _(i))  (8-776)

The predicted luma sample value predSampleLx_(L) is derived as follows:

-   -   If both xFrac_(L) and yFrac_(L) are equal to 0, the value of        predSampleLx_(L) is derived as follows:

predSampleLx _(L) =refPicLx _(L)[xInt ₃][yInt ₃]<<shift3  (8-777)

-   -   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is equal        to 0, the value of predSampleLx_(L) is derived as follows:

predSampleLx _(L)=(Σ_(i=0) ⁷ f _(L)[xFrac _(L)][i]*refPicLx _(L)[xInt_(i)][yInt ₃])>>shift1  (8-778)

-   -   Otherwise, if xFrac_(L) is equal to 0 and yFrac_(L) is not equal        to 0, the value of predSampleLx_(L) is derived as follows:

predSampleLx _(L)=(Σ_(i=0) ⁷ f _(L)[yFrac _(L)][i]*refPicLx _(L)[xInt₃][yInt _(i)])>>shift1  (8-779)

-   -   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is not        equal to 0, the value of predSampleLx_(L) is derived as follows:        -   The sample array temp[n] with n=0 . . . 7, is derived as            follows:

temp[n]=(Σ_(i=0) ⁷ f _(L)[xFrac _(L)][i]*refPicLx _(L)[xInt _(i)][yInt_(n)])>>shift1  (8-780)

-   -   -   The predicted luma sample value predSampleLx_(L) is derived            as follows:

predSampleLx _(L)=(Σ_(i=0) ⁷ f _(L)[yFrac_(L)][i]*temp[i])>>shift2  (8-781)

TABLE 8-11 Specification of the luma interpolation filter coefficientsf_(L)[ p ] for each 1/16 fractional sample position p. Fractional sampleinterpolation filter coefficients position p f_(L)[ p ][ 0 ] f_(L)[ p ][1 ] f_(L)[ p ][ 2 ] f_(L)[ p ][ 3 ] f_(L)[ p ][ 4 ] f_(L)[ p ][ 5 ]f_(L)[ p ][ 6 ] f_(L)[ p ][ 7 ]  1 0 1 −3 63 4 −2 1 0 2 −1 2 −5 62 8 −31 0 3 −1 3 −8 60 13 −4 1 0 4 −1 4 −10 58 17 −5 1 0 5 −1 4 −11 52 26 −8 3−1 6 −1 3 −9 47 31 −10 4 −1 7 −1 4 −11 45 34 −10 4 −1 8 −1 4 −11 40 40−11 4 −1 (hpelIfIdx = = 0) 8 0 3 9 20 20 9 3 0 (hpelIfIdx = = 1) 9 −1 4−10 34 45 −11 4 −1 10 −1 4 −10 31 47 −9 3 −1 11 −1 3 −8 26 52 −11 4 −112 0 1 −5 17 58 −10 4 −1 13 0 1 −4 13 60 −8 3 −1 14 0 1 −3 8 62 −5 2 −115 0 1 −2 4 63 −3 1 0

TABLE 8-12 Specification of the luma interpolation filter coefficientsf_(L)[ p ] for each 1/16 fractional sample position p for affine motionmode. Fractional sample interpolation filter coefficients position pf_(L)[ p ][ 0 ] f_(L)[ p ][ 1 ] f_(L)[ p ][ 2 ] f_(L)[ p ][ 3 ] f_(L)[ p][ 4 ] f_(L)[ p ][ 5 ] f_(L)[ p ][ 6 ] f_(L)[ p ][ 7 ] 1 0 1 −3 63 4 −21 0 2 0 1 −5 62 8 −3 1 0 3 0 2 −8 60 13 −4 1 0 4 0 3 −10 58 17 −5 1 0 50 3 −11 52 26 −8 2 0 6 0 2 −9 47 31 −10 3 0 7 0 3 −11 45 34 −10 3 0 8 03 −11 40 40 −11 3 0 9 0 3 −10 34 45 −11 3 0 10 0 3 −10 31 47 −9 2 0 11 02 −8 26 52 −11 3 0 12 0 1 −5 17 58 −10 3 0 13 0 1 −4 13 60 −8 2 0 14 0 1−3 8 62 −5 1 0 15 0 1 −2 4 63 −3 1 0

FIG. 30 is a flowchart for a method 3000 for video processing. Themethod 3000 includes, at operation 3010, determining, for a conversionbetween a current block of video and a bitstream representation of thevideo, a maximum number of candidates (ML) in a sub-block based mergecandidate list and/or whether to add sub-block based temporal motionvector prediction (SbTMVP) candidates to the sub-block based mergecandidate list based on whether temporal motion vector prediction (TMVP)is enabled for use during the conversion or whether a current picturereferencing (CPR) coding mode is used for the conversion.

The method 3000 includes, at operation 3020, performing, based on thedetermining, the conversion.

FIG. 31 is a flowchart for a method 3100 for video processing. Themethod 3100 includes, at operation 3110, determining, for a conversionbetween a current block of video and a bitstream representation of thevideo, a maximum number of candidates (ML) in a sub-block based mergecandidate list based on whether a temporal motion vector prediction(TMVP), a sub-block based temporal motion vector prediction (SbTMVP),and an affine coding mode are enabled for use during the conversion.

The method 3100 includes, at operation 3120, performing, based on thedetermining, the conversion.

FIG. 32 is a flowchart for a method 3200 for video processing. Themethod 3200 includes, at operation 3210, determining, for a conversionbetween a current block of a first video segment of a video and abitstream representation of the video, that a sub-block based motionvector prediction (SbTMVP) mode is disabled for the conversion due to atemporal motion vector prediction (TMVP) mode being disabled at a firstvideo segment level.

The method 3200 includes, at operation 3220, performing the conversionbased on the determining, the bitstream representation complying with aformat that specifies whether an indication of the SbTMVP mode isincluded and/or a position of the indication of the SbTMVP mode in amerge candidate list, with respect to an indication of the TMVP mode.

FIG. 33 is a flowchart for a method 3300 for video processing. Themethod 3300 includes, at operation 3310, performing a conversion betweena current block of a video that is coded using a sub-block basedtemporal motion vector prediction (SbTMVP) tool or a temporal motionvector prediction (TMVP) tool and a bitstream representation of thevideo, a coordinate of a corresponding position of the current block ora sub-block of the current block being selectively masked using a maskbased on a compression of motion vectors associated with the SbTMVP toolor the TMVP tool, and an application of the mask comprising computing abitwise AND operation between a value of the coordinate and a value ofthe mask.

FIG. 34 is a flowchart for a method 3400 for video processing. Themethod 3400 includes, at operation 3410, determining, based on one ormore characteristics of a current block of a video segment of a video, avalid corresponding region of the current block for an application of asub-block based motion vector prediction (SbTMVP) tool on the currentblock.

The method 3400 includes, at operation 3420, performing, based on thedetermining, a conversion between the current block and a bitstreamrepresentation of the video.

FIG. 35 is a flowchart for a method 3500 for video processing. Themethod 3500 includes, at operation 3510, determining, for a currentblock of a video that is coded using a sub-block based temporal motionvector prediction (SbTMVP) tool, a default motion vector.

The method 3500 includes, at operation 3520, performing, based on thedetermining, a conversion between the current block and a bitstreamrepresentation of the video, the default motion vector being determinedin case that a motion vector is not obtained from a block covering acorresponding position in the collocated picture that is associated witha center position of the current block.

FIG. 36 is a flowchart for a method 3600 for video processing. Themethod 3600 includes, at operation 3610, inferring, for a current blockof a video segment of a video, that a sub-block based temporal motionvector prediction (SbTMVP) tool or a temporal motion vector prediction(TMVP) tool is disabled for the video segment in case that a currentpicture of the current block is a reference picture with an index set toM in a reference picture list X, M and X being integers, and X=0 or X=1.

The method 3600 includes, at operation 3620, performing, based on theinferring, a conversion between the current block and a bitstreamrepresentation of the video.

FIG. 37 is a flowchart for a method 3700 for video processing. Themethod 3700 includes, at operation 3710, determining, for a currentblock of a video, that an application of an sub-block based temporalmotion vector prediction (SbTMVP) tool is enabled in case that a currentpicture of the current block is a reference picture with an index set toM in a reference picture list X, M and X being integers.

The method 3700 includes, at operation 3720, performing, based on thedetermining, a conversion between the current block and a bitstreamrepresentation of the video.

FIG. 38 is a flowchart for a method 3800 for video processing. Themethod 3800 includes, at operation 3810, performing a conversion betweena current block of a video and a bitstream representation of the video,the current block being coded using a sub-block based coding tool,wherein performing the conversion comprises using a plurality of bins(N) to code a sub-block merge index with a unified method in case that asub-block based temporal motion vector prediction (SbTMVP) tool isenabled or disabled.

FIG. 39 is a flowchart for a method 3900 for video processing. Themethod 3900 includes, at operation 3910, determining, for a currentblock of a video coded using a sub-block based temporal motion vectorprediction (SbTMVP) tool, a motion vector used by the SbTMVP tool tolocate a corresponding block in a picture different from a currentpicture comprising the current block.

The method 3900 includes, at operation 3920, performing, based on thedetermining, a conversion between the current block and a bitstreamrepresentation of the video.

FIG. 40 is a flowchart for a method 4000 for video processing. Themethod 4000 includes, at operation 4010, determining, for a conversionbetween a current block of a video and a bitstream representation of thevideo, whether a zero motion affine merge candidate is inserted into asub-block merge candidate list based on whether affine prediction isenabled for the conversion of the current block.

The method 4000 includes, at operation 4020, performing, based on thedetermining, the conversion.

FIG. 41 is a flowchart for a method 4100 for video processing. Themethod 4100 includes, at operation 4110, inserting, for a conversionbetween a current block of a video and a bitstream representation of thevideo that uses a sub-block merge candidate list, zero motion non-affinepadding candidates into the sub-block merge candidate list in case thatthe sub-block merge candidate list is not fulfilled.

The method 4100 includes, at operation 4120, performing, subsequent tothe inserting, the conversion.

FIG. 42 is a flowchart for a method 4200 for video processing. Themethod 4200 includes, at operation 4210, determining, for a conversionbetween a current block of a video and a bitstream representation of thevideo, motion vectors using a rule that determines that the motionvectors are derived from one or more motion vectors of a block coveringa corresponding position in a collocated picture.

The method 4200 includes, at operation 4220, performing, based on themotion vectors, the conversion.

FIG. 43 is a block diagram of a video processing apparatus 4300. Theapparatus 4300 may be used to implement one or more of the methodsdescribed herein. The apparatus 4300 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 4300 may include one or more processors 4302, one or morememories 4304 and video processing hardware 4306. The processor(s) 4302may be configured to implement one or more methods described in thepresent document. The memory (memories) 4304 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 4306 may be used to implement, inhardware circuitry, some techniques described in the present document.

In some embodiments, the video coding methods may be implemented usingan apparatus that is implemented on a hardware platform as describedwith respect to FIG. 43.

Some embodiments of the disclosed technology include making a decisionor determination to enable a video processing tool or mode. In anexample, when the video processing tool or mode is enabled, the encoderwill use or implement the tool or mode in the processing of a block ofvideo, but may not necessarily modify the resulting bitstream based onthe usage of the tool or mode. That is, a conversion from the block ofvideo to the bitstream representation of the video will use the videoprocessing tool or mode when it is enabled based on the decision ordetermination. In another example, when the video processing tool ormode is enabled, the decoder will process the bitstream with theknowledge that the bitstream has been modified based on the videoprocessing tool or mode. That is, a conversion from the bitstreamrepresentation of the video to the block of video will be performedusing the video processing tool or mode that was enabled based on thedecision or determination.

Some embodiments of the disclosed technology include making a decisionor determination to disable a video processing tool or mode. In anexample, when the video processing tool or mode is disabled, the encoderwill not use the tool or mode in the conversion of the block of video tothe bitstream representation of the video. In another example, when thevideo processing tool or mode is disabled, the decoder will process thebitstream with the knowledge that the bitstream has not been modifiedusing the video processing tool or mode that was enabled based on thedecision or determination.

FIG. 44 is a block diagram showing an example video processing system4400 in which various techniques disclosed herein may be implemented.Various implementations may include some or all of the components of thesystem 4400. The system 4400 may include input 4402 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 4402 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 4400 may include a coding component 4404 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 4404 may reduce the average bitrate ofvideo from the input 4402 to the output of the coding component 4404 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 4404 may be eitherstored, or transmitted via a communication connected, as represented bythe component 4406. The stored or communicated bitstream (or coded)representation of the video received at the input 4402 may be used bythe component 4408 for generating pixel values or displayable video thatis sent to a display interface 4410. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include SATA (serial advanced technology attachment), PCI,IDE interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

In some embodiments, the following technical solutions can beimplemented:

A1. A method of video processing, comprising: determining, for aconversion between a current block of video and a bitstreamrepresentation of the video, a maximum number of candidates (ML) in asub-block based merge candidate list and/or whether to add sub-blockbased temporal motion vector prediction (SbTMVP) candidates to thesub-block based merge candidate list based on whether temporal motionvector prediction (TMVP) is enabled for use during the conversion orwhether a current picture referencing (CPR) coding mode is used for theconversion; and performing, based on the determining, the conversion.

A2. The method of solution A1, wherein the use of the SbTMVP candidatesis disabled due to a determination that the TMVP tool is disabled or anSbTMVP tool is disabled.

A3. The method of solution A2, wherein determining ML comprises:excluding the SbTMVP candidates from the sub-block based merge candidatelist based on whether the SbTMVP tool or the TMVP tool are disabled.

A4. A method of video processing, comprising: determining, for aconversion between a current block of video and a bitstreamrepresentation of the video, a maximum number of candidates (ML) in asub-block based merge candidate list based on whether a temporal motionvector prediction (TMVP), a sub-block based temporal motion vectorprediction (SbTMVP), and an affine coding mode are enabled for useduring the conversion; and performing, based on the determining, theconversion.

A5. The method of solution A4, wherein ML is set on-the-fly and signaledin the bitstream representation due to a determination that the affinecoding mode is enabled.

A6. The method of solution A4, wherein ML is predefined due to adetermination that the affine coding mode is disabled.

A7. The method of solution A2 or A6, wherein determining ML comprises:setting ML to zero due to a determination that the TMVP tool isdisabled, an SbTMVP tool is enabled and the affine coding mode for thecurrent block is disabled.

A8. The method of solution A2 or A6, wherein determining ML comprises:setting ML to one due to a determination that an SbTMVP tool is enabled,the TMVP tool is enabled and the affine coding mode for the currentblock is disabled.

A9. The method of solution A₁, wherein the use of the SbTMVP candidatesis disabled due to a determination that a SbTMVP tool is disabled or acollocated reference picture of a current picture of the current blockis the current picture.

A10. The method of solution A9, wherein determining ML comprises:excluding the SbTMVP candidates from the sub-block based merge candidatelist based on whether the SbTMVP tool is disabled or the collocatedreference picture of the current picture is the current picture.

A11. The method of solution A9, wherein determining ML comprises:setting ML to zero due to a determination that the collocated referencepicture of the current picture is the current picture, and affine codingfor the current block is disabled.

A12. The method of solution A9, wherein determining ML comprises:setting ML to one due to a determination that the SbTMVP tool isenabled, the collocated reference picture of the current picture is notthe current picture, and affine coding for the current block isdisabled.

A13. The method of solution A1, wherein the use of the SbTMVP candidatesis disabled due to a determination that an SbTMVP tool is disabled or areference picture with reference picture index 0 in reference picturelist 0 (L0) is a current picture of the current block.

A14. The method of solution A13, wherein determining ML comprises:excluding the SbTMVP candidates from the sub-block based merge candidatelist based on whether the SbTMVP tool is disabled or the referencepicture with reference picture index 0 in L0 is the current picture.

A15. The method of solution A10 or A13 wherein determining ML comprises:setting ML to zero due to a determination that the SbTMVP tool isenabled, the reference picture with reference picture index 0 in L0 isthe current picture, and affine coding for the current block isdisabled.

A16. The method of solution A13, wherein determining ML comprises:setting ML to one due to a determination that the SbTMVP tool isenabled, the reference picture with reference picture index 0 in L0 isnot the current picture, and affine coding for the current block isdisabled.

A17. The method of solution A1, wherein the use of the SbTMVP candidatesis disabled due to a determination that a SbTMVP tool is disabled or areference picture with reference picture index 0 in reference picturelist 1 (L1) is a current picture of the current block.

A18. The method of solution A17, wherein determining ML comprises:excluding the SbTMVP candidates from the sub-block based merge candidatelist based on whether the SbTMVP tool is disabled or the referencepicture with reference picture index 0 in L1 is the current picture.

A19. The method of solution A17, wherein determining ML comprises:setting ML to zero due to a determination that the SbTMVP tool isenabled, the reference picture with reference picture index 0 in L1 isthe current picture, and affine coding for the current block isdisabled.

A20. The method of solution A17, wherein determining ML comprises:setting ML to one due to a determination that the SbTMVP tool isenabled, the reference picture with reference picture index 0 in L1 isnot the current picture, and affine coding for the current block isdisabled.

A21. A method of video processing, comprising: determining, for aconversion between a current block of a first video segment of a videoand a bitstream representation of the video, that a sub-block basedmotion vector prediction (SbTMVP) mode is disabled for the conversiondue to a temporal motion vector prediction (TMVP) mode being disabled ata first video segment level; and performing the conversion based on thedetermining, wherein the bitstream representation complies with a formatthat specifies whether an indication of the SbTMVP mode is includedand/or a position of the indication of the SbTMVP mode in a mergecandidate list, with respect to an indication of the TMVP mode.

A22. The method of solution A21, wherein the first video segment is asequence, slice, a tile or a picture.

A23. The method of solution A21, wherein the format specifies anomission of the indication of the SbTMVP mode due to an inclusion of theindication of the TMVP mode at the first video segment level.

A24. The method of solution A21, wherein the format specifies that theindication of the SbTMVP mode is at the first video segment level afterthe indication of the TMVP mode in a decoding order.

A25. The method of any of solutions A21 to A24, wherein the formatspecifies that the indication of the SbTMVP mode is omitted due to adetermination that the TMVP mode is indicated as being disabled.

A26. The method of solution A21, wherein the format specifies that theindication of the SbTMVP mode is included at a sequence level for thevideo and omitted at a second video segment level.

A27. The method of solution A26, wherein a second video segment at thesecond video segment level is a slice, a tile or a picture.

A28. The method of any of solutions A1 to A27, the conversion generatesthe current block from the bitstream representation.

A29. The method of any of solutions A1 to A27, wherein the conversiongenerates the bitstream representation from the current block.

A30. The method of any of solutions A1 to A27, wherein performing theconversion comprises parsing the bitstream representation based on oneor more decoding rules.

A31. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method in any one of solutions A1 to A30.

A32. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method in any one of solutions A1 to A30.

In some embodiments, the following technical solutions can beimplemented:

B1. A method of video processing, comprising: performing a conversionbetween a current block of a video that is coded using a sub-block basedtemporal motion vector prediction (SbTMVP) tool or a temporal motionvector prediction (TMVP) tool and a bitstream representation of thevideo, wherein a coordinate of a corresponding position of the currentblock or a sub-block of the current block is selectively masked using amask based on a compression of motion vectors associated with the SbTMVPtool or the TMVP tool, and wherein an application of the mask comprisescomputing a bitwise AND operation between a value of the coordinate anda value of the mask.

B2. The method of solution B1, wherein the coordinate is (xN, yN) andthe mask (MASK) is an integer equal to ˜(2M−1), wherein M is an integer,wherein the application of the mask results in a masked coordinate (xN′,yN′), wherein xN′=xN&MASK and yN′=yN&MASK, and wherein “˜” is thebitwise NOT operation and “&” is the bitwise AND operation.

B3. The method of solution B2, wherein M=3 or M=4.

B4. The method of solution B2 or B3, wherein a plurality of sub-blocksof size 2K×2K share a same motion information based on the compressionof the motion vectors, and wherein K is an integer not equal to M.

B5. The method of solution B4, wherein M=K+1.

B6. The method of solution B1, wherein the mask is not applied upon adetermination that the motion vectors associated with the SbTMVP tool orthe TMVP tool are not compressed.

B7. The method of any of solutions B1 to B6, wherein the mask for theSbTMVP tool is identical to the mask for the TMVP tool.

B8. The method of any of solutions B1 to B6, wherein the mask for theATMVP tool is different from the mask for the TMVP tool.

B9. The method of solution B1, wherein a type of the compression is nocompression, 8×8 compression or 16×16 compression.

B10. The method of solution B9, wherein the type of the compression issignaled in a video parameter set (VPS), a sequence parameter set (SPS),a picture parameter set (PPS), a slice header or a tile group header.

B11. The method of solution B9 or B10, wherein the type of thecompression is based on a standard profile, level or tier correspondingto the current block.

B12. A method of video processing, comprising: determining, based on oneor more characteristics of a current block of a video segment of avideo, a valid corresponding region of the current block for anapplication of a sub-block based motion vector prediction (SbTMVP) toolon the current block; and performing, based on the determining, aconversion between the current block and a bitstream representation ofthe video.

B13. The method of solution B12, wherein the one or more characteristicscomprises a height or a width of the current block.

B14. The method of solution B12, wherein the one or more characteristicscomprises a type of a compression of motion vectors associated with thecurrent block.

B15. The method of solution B14, wherein the valid corresponding regionis a first size due to a determination that the type of the compressioncomprises no compression, and wherein the valid corresponding region isa second size that is larger than the first size due to a determinationthat the type of compression comprises K×K compression.

B16. The method of solution B12, wherein a size of the validcorresponding region is based on a basic region with size M×N that issmaller than a size of a coding tree unit (CTU) region, and wherein asize of the current block is W×H.

B17. The method of solution B16, wherein the size of the CTU region is128×128, and wherein M=64 and N=64.

B18. The method of solution B16, wherein the valid corresponding regionis a collocated basic region and an extension in a collocated picturedue to a determination that W<M and H<N.

B19. The method of solution B16, wherein the current block ispartitioned into several parts upon a determination that W>M and H>N,and wherein each of the several parts comprises an individual validcorresponding region for the application of the SbTMVP tool.

B20. A method of video processing, comprising: determining, for acurrent block of a video that is coded using a sub-block based temporalmotion vector prediction (SbTMVP) tool, a default motion vector; andperforming, based on the determining, a conversion between the currentblock and a bitstream representation of the video, wherein the defaultmotion vector is determined due to a determination that a motion vectoris not obtained from a block covering a corresponding position in thecollocated picture that is associated with a center position of thecurrent block.

B21. The method of solution B20, wherein the default motion vector isset to (0, 0).

B22. The method of solution B20, wherein the default motion vector isderived from a history-based motion vector prediction (HMVP) table.

B23. The method of solution B22, wherein the default motion vector isset to (0, 0) due to a determination that the HMVP table is empty.

B24. The method of solution B22, wherein the default motion vector ispredefined and signaled in a video parameter set (VPS), a sequenceparameter set (SPS), a picture parameter set (PPS), a slice header, atile group header, a coding tree unit (CTU) or a coding unit (CU).

B25. The method of solution B22, wherein the default motion vector isset to a first element stored in the HMVP table due to a determinationthat the HMVP table is non-empty.

B26. The method of solution B22, wherein the default motion vector isset to a last element stored in the HMVP table due to a determinationthat the HMVP table is non-empty.

B27. The method of solution B22, wherein the default motion vector isset to a specific motion vector stored in the HMVP table due to adetermination that the HMVP table is non-empty.

B28. The method of solution B27, wherein the specific motion vectorrefers to reference list 0.

B29. The method of solution B27, wherein the specific motion vectorrefers to reference list 1.

B30. The method of solution B27, wherein the specific motion vectorrefers to a specific reference picture in reference list 0.

B31. The method of solution B27, wherein the specific motion vectorrefers to a specific reference picture in reference list 1.

B32. The method of solution B30 or B31, wherein the specific referencepicture has index 0.

B33. The method of solution B27, wherein the specific motion vectorrefers to a collocated picture.

B34. The method of solution B22, wherein the default motion vector isset to a predefined default motion vector due to a determination that asearch process in the HMVP table cannot find a specific motion vector.

B35. The method of solution B34, wherein the search process searchesonly the first element or only the last element of the HMVP table.

B36. The method of solution B34, wherein the search process searchesonly a subset of elements of the HMVP table.

B37. The method of solution B22, wherein the default motion vector doesnot refer to a current picture of the current block.

B38. The method of solution B22, wherein the default motion vector isscaled to a collocated picture due to a determination that the defaultmotion vector does not refer to the collocated picture.

B39. The method of solution B20, wherein the default motion vector isderived from a neighboring block.

B40. The method of solution B39, wherein an upper right corner of theneighboring block (A0) is directly adjacent to a lower left corner tothe current block, or a lower right corner of the neighboring block (A1)is directly adjacent to the lower left corner to the current block, or alower left corner of the neighboring block (B0) is directly adjacent toan upper right corner of the current block, or a lower right corner ofthe neighboring block (B1) is directly adjacent to the upper rightcorner of the current block, or a lower right corner of the neighboringblock (B2) is directly adjacent to an upper left corner of the currentblock.

B41. The method of solution B40, wherein the default motion vector isderived from only one of neighboring blocks A0, A1, B0, B1 and B2.

B42. The method of solution B40, wherein the default motion vector isderived from one or more of neighboring blocks A0, A1, B0, B1 and B2.

B43. The method of solution B40, wherein the default motion vector isset to a predefined default motion vector due to a determination that avalid default motion vector cannot be found in any of the neighboringblocks A0, A1, B0, B1 and B2.

B44. The method of solution B43, wherein the predefined default motionvector is signaled in a video parameter set (VPS), a sequence parameterset (SPS), a picture parameter set (PPS), a slice header, a tile groupheader, a coding tree unit (CTU) or a coding unit (CU).

B45. The method of solution B43 or B44, wherein the predefined defaultmotion vector is (0, 0).

B46. The method of solution B39, wherein the default motion vector isset to a specific motion vector from the neighboring block.

B47. The method of solution B46, wherein the specific motion vectorrefers to reference list 0.

B48. The method of solution B46, wherein the specific motion vectorrefers to reference list 1.

B49. The method of solution B46, wherein the specific motion vectorrefers to a specific reference picture in reference list 0.

B50. The method of solution B46, wherein the specific motion vectorrefers to a specific reference picture in reference list 1.

B51. The method of solution B49 or B50, wherein the specific referencepicture has index 0.

B52. The method of solution B46, wherein the specific motion vectorrefers to a collocated picture.

B53. The method of solution B20, wherein the default motion vector isused due to a determination that the block covering the correspondingposition in the collocated picture is intra-coded.

B54. The method of solution B20, wherein the derivation method ismodified due to a determination that the block covering thecorresponding position in the collocated picture is not located.

B55. The method of solution B20, wherein a default motion vectorcandidate is always available.

B56. The method of solution B20, wherein the default motion vector isderived in an alternate manner upon a determination that a defaultmotion vector candidate is set to unavailable.

B57. The method of solution B20, wherein an availability of the defaultmotion vector is based on syntax information in the bitstreamrepresentation associated with the video segment.

B58. The method of solution B57, wherein the syntax informationcomprises an indication of enabling the SbTMVP tool, and wherein thevideo segment is a slice, a tile or a picture.

B59. The method of solution B58, wherein a current picture of thecurrent block is not an intra random access point (IRAP) picture and thecurrent picture is not inserted to a reference picture list 0 (L0) witha reference index 0.

B60. The method of solution B20, wherein a fixed index or a fixed groupof indices is assigned to candidates associated with the SbTMVP tool dueto a determination that the SbTMVP tool is enabled, and wherein thefixed index or the fixed group of indices is assigned to candidatesassociated with a coding tool other than the SbTMVP tool due to adetermination that the SbTMVP tool is disabled.

B61. A method of video processing, comprising: inferring, for a currentblock of a video segment of a video, that a sub-block based temporalmotion vector prediction (SbTMVP) tool or a temporal motion vectorprediction (TMVP) tool is disabled for the video segment due to adetermination that a current picture of the current block is a referencepicture with an index set to M in a reference picture list X, wherein Mand X are integers, and wherein X=0 or X=1; and performing, based on theinferring, a conversion between the current block and a bitstreamrepresentation of the video.

B62. The method of solution B61, wherein M corresponds to a targetreference picture index that motion information of a temporal block isscaled to for the reference picture list X for the SbTMVP tool or theTMVP tool.

B63. The method of solution B61, wherein the current picture is an intrarandom access point (IRAP) picture.

B64. A method of video processing, comprising: determining, for acurrent block of a video, that an application of an sub-block basedtemporal motion vector prediction (SbTMVP) tool is enabled due to adetermination that a current picture of the current block is a referencepicture with an index set to M in a reference picture list X, wherein Mand X are integers; and performing, based on the determining, aconversion between the current block and a bitstream representation ofthe video.

B65. The method of solution B64, wherein motion informationcorresponding to each sub-block of the current block refers to thecurrent picture.

B66. The method of solution B64, wherein motion information for asub-block of the current block is derived from a temporal block, andwherein the temporal block is coded with at least one reference picturethat refers to a current picture of the temporal block.

B67. The method of solution B66, wherein the conversion excludes ascaling operation.

B68. A method of video processing, comprising: performing a conversionbetween a current block of a video and a bitstream representation of thevideo, wherein the current block is coded using a sub-block based codingtool, and wherein performing the conversion comprises using a pluralityof bins (N) to code a sub-block merge index with a unified method due toa determination that a sub-block based temporal motion vector prediction(SbTMVP) tool is enabled or disabled.

B69. The method of solution B68, wherein a first number of bins (L) ofthe plurality of bins are context coded, and wherein a second number ofbins (N-L) are bypass coded.

B70. The method of solution B69, wherein L=1.

B71. The method of solution B68, wherein each of the plurality of binsis context coded.

B72. The method of any of solutions B1 to B71, the conversion generatesthe current block from the bitstream representation.

B73. The method of any of solutions B1 to B71, wherein the conversiongenerates the bitstream representation from the current block.

B74. The method of any of solutions B1 to B71, wherein performing theconversion comprises parsing the bitstream representation based on oneor more decoding rules.

B75. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method in any one of solutions B1 to B74.

B76. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method in any one of solutions B1 to B74.

In some embodiments, the following technical solutions can beimplemented:

C1. A method of video processing, comprising: determining, for a currentblock of a video coded using a subblock-based temporal motion vectorprediction (SbTMVP) tool, a motion vector used by the SbTMVP tool tolocate a corresponding block in a picture different from a currentpicture comprising the current block; and performing, based on thedetermining, a conversion between the current block and a bitstreamrepresentation of the video.

C2. The method of solution C1, wherein the motion vector is set to adefault motion vector.

C3. The method of solution C2, wherein the default motion vector is (0,0).

C4. The method of solution C2, wherein the default motion vector issignaled in a video parameter set (VPS), a sequence parameter set (SPS),a picture parameter set (PPS), a slice header, a tile group header, acoding tree unit (CTU) or a coding unit (CU).

C5. The method of solution C1, wherein motion vector is set to a motionvector stored in a history-based motion vector prediction (HMVP) table.

C6. The method of solution C5, wherein the motion vector is set to adefault motion vector due to a determination that the HMVP table isempty.

C7. The method of solution C6, wherein the default motion vector is (0,0).

C8. The method of solution C5, wherein the motion vector is set to afirst motion vector stored in the HMVP table due to a determination thatthe HMVP table is non-empty.

C9. The method of solution C5, wherein the motion vector is set to alast motion vector stored in the HMVP table due to a determination thatthe HMVP table is non-empty.

C10. The method of solution C5, wherein the motion vector is set to aspecific motion vector stored in the HMVP table due to a determinationthat the HMVP table is non-empty.

C11. The method of solution C10, wherein the specific motion vectorrefers to reference list 0.

C12. The method of solution C10, wherein the specific motion vectorrefers to reference list 1.

C13. The method of solution C10, wherein the specific motion vectorrefers to a specific reference picture in reference list 0.

C14. The method of solution C10, wherein the specific motion vectorrefers to a specific reference picture in reference list 1.

C15. The method of solution C13 or 14, wherein the specific referencepicture has index 0.

C16. The method of solution C10, wherein the specific motion vectorrefers to a collocated picture.

C17. The method of solution C5, wherein the motion vector is set to adefault motion vector due to a determination that a search process inthe HMVP table cannot find a specific motion vector.

C18. The method of solution C17, wherein the search process searchesonly the first element or only the last element of the HMVP table.

C19. The method of solution C17, wherein the search process searchesonly a subset of elements of the HMVP table.

C20. The method of solution C5, wherein the motion vector stored in theHMVP table does not refer to the current picture.

C21. The method of solution C5, wherein the motion vector stored in theHMVP table is scaled to a collocated picture due to a determination thatthe motion vector stored in the HMVP table does not refer to thecollocated picture.

C22. The method of solution C1, wherein the motion vector is set to aspecific motion vector of a specific neighboring block.

C23. The method of solution C22, wherein an upper right corner of thespecific neighboring block (A0) is directly adjacent to a lower leftcorner to the current block, or a lower right corner of the specificneighboring block (A1) is directly adjacent to the lower left corner tothe current block, or a lower left corner of the specific neighboringblock (B0) is directly adjacent to an upper right corner of the currentblock, or a lower right corner of the specific neighboring block (B1) isdirectly adjacent to the upper right corner of the current block, or alower right corner of the specific neighboring block (B2) is directlyadjacent to an upper left corner of the current block.

C24. The method of solution C1, wherein the motion vector is set to adefault motion vector due to a determination that a specific neighboringblock does not exist.

C25. The method of solution C1, wherein the motion vector is set to adefault motion vector due to a determination that a specific neighboringblock is not inter-coded.

C26. The method of solution C22, wherein the specific motion vectorrefers to reference list 0.

C27. The method of solution C22, wherein the specific motion vectorrefers to reference list 1.

C28. The method of solution C22, wherein the specific motion vectorrefers to a specific reference picture in reference list 0.

C29. The method of solution C22, wherein the specific motion vectorrefers to a specific reference picture in reference list 1.

C30. The method of solution C28 or C29, wherein the specific referencepicture has index 0.

C31. The method of solution C22 or C23, wherein the specific motionvector refers to a collocated picture.

C32. The method of solution C22 or C23, wherein the motion vector is setto a default motion vector due to a determination that the specificneighboring block does not refer to the collocated picture.

C33. The method of any of solutions C24 to C32, wherein the defaultmotion vector is (0, 0).

C34. The method of solution C1, wherein the motion vector is set to adefault motion vector due to a determination that a specific motionvector stored in a specific neighboring block cannot be found.

C35. The method of solution C22, wherein the specific motion vector isscaled to a collocated picture due to a determination that the specificmotion vector not refer to the collocated picture.

C36. The method of solution C22, wherein the specific motion vector doesnot refer to the current picture.

C37. The method of any of solutions C1 to C36, the conversion generatesthe current block from the bitstream representation.

C38. The method of any of solutions C1 to C36, wherein the conversiongenerates the bitstream representation from the current block.

C39. The method of any of solutions C1 to C36, wherein performing theconversion comprises parsing the bitstream representation based on oneor more decoding rules.

C40. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method in any one of solutions C1 to C39.

C41. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method in any one of solutions C1 to C39.

In some embodiments, the following technical solutions can beimplemented:

D1. A method of video processing, comprising: determining, for aconversion between a current block of a video and a bitstreamrepresentation of the video, whether a zero motion affine mergecandidate is inserted into a sub-block merge candidate list based onwhether affine prediction is enabled for the conversion of the currentblock; and performing, based on the determining, the conversion.

D2. The method of solution D1, wherein the zero motion affine mergecandidate is not inserted into the sub-block merge candidate list due toa determination that an affine usage flag in the bitstreamrepresentation is off.

D3. The method of solution D2, further comprising: inserting defaultmotion vector candidates that are non-affine candidates into thesub-block merge candidate list due to a determination that the affineusage flag is off.

D4. A method of video processing, comprising: inserting, for aconversion between a current block of a video and a bitstreamrepresentation of the video that uses a sub-block merge candidate list,zero motion non-affine padding candidates into the sub-block mergecandidate list due to a determination that the sub-block merge candidatelist is not fulfilled; and performing, subsequent to the inserting, theconversion.

D5. The method of solution D4, further comprising: setting an affineusage flag of the current block to zero.

D6. The method of solution D4, wherein the inserting is further based onwhether an affine usage flag in the bitstream representation is off.

D7. A method of video processing, comprising: determining, for aconversion between a current block of a video and a bitstreamrepresentation of the video, motion vectors using a rule that determinesthat the motion vectors are derived from one or more motion vectors of ablock covering a corresponding position in a collocated picture; andperforming, based on the motion vectors, the conversion.

D8. The method of solution D7, wherein the one or more motion vectorscomprise MV0 and MV1 that represent motion vectors in reference list 0and reference list 1, respectively, and wherein the motion vectors to bederived comprise MV0′ and MV1′ that that represent motion vectors in thereference list 0 and the reference list 1.

D9. The method of solution D8, wherein MV0′ and MV1′ are derived basedon MV0 due to a determination that a collocated picture is in thereference list 0.

D10. The method of solution D8, wherein MV0′ and MV1′ are derived basedon MV1 due to a determination that a collocated picture is in thereference list 1.

D11. The method of any of solutions D1 to D10, the conversion generatesthe current block from the bitstream representation.

D12. The method of any of solutions D1 to D10, wherein the conversiongenerates the bitstream representation from the current block.

D13. The method of any of solutions D1 to D10, wherein performing theconversion comprises parsing the bitstream representation based on oneor more decoding rules.

D14. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method in any one of solutions D1 to D13.

D15. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method in any one of solutions D1 to D13.

The disclosed and other solutions, examples, embodiments, modules andthe functional operations described in this document can be implementedin digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this document and theirstructural equivalents, or in combinations of one or more of them. Thedisclosed and other embodiments can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a computer readable medium for execution by, orto control the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any subject matter or of whatmay be claimed, but rather as descriptions of features that may bespecific to particular embodiments of particular techniques. Certainfeatures that are described in this patent document in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

1. A method of video processing, comprising: inserting, for a conversionbetween a current block of a video and a bitstream of the video thatuses a sub-block merge candidate list, zero motion non-affine paddingcandidates into the sub-block merge candidate list in case that thesub-block merge candidate list is not fulfilled; and performing,subsequent to the inserting, the conversion.
 2. The method of claim 1,further comprising: setting an affine usage flag of the current block tozero.
 3. The method of claim 1, wherein the inserting is further basedon whether an affine usage flag in the bitstream is off.
 4. The methodof claim 1, further comprising: determining whether a zero motion affinemerge candidate is inserted into the sub-block merge candidate listbased on whether affine prediction is enabled for the conversion of thecurrent block.
 5. The method of claim 4, wherein the zero motion affinemerge candidate is not inserted into the sub-block merge candidate listin case that an affine usage flag in the bitstream is off.
 6. The methodof claim 5, further comprising: inserting default motion vectorcandidates that are non-affine candidates into the sub-block mergecandidate list in case that the affine usage flag is off.
 7. The methodof claim 1, further comprising: determining motion vectors using a rulethat determines that the motion vectors are derived from one or moremotion vectors of a block covering a corresponding position in acollocated picture.
 8. The method of claim 7, wherein the one or moremotion vectors comprise MV0 and MV1 that represent motion vectors inreference list 0 and reference list 1, respectively, and wherein themotion vectors to be derived comprise MV0′ and MV1′ that that representmotion vectors in the reference list 0 and the reference list
 1. 9. Themethod of claim 8, wherein MV0′ and MV1′ are derived based on MV0 incase that a collocated picture is in the reference list
 0. 10. Themethod of claim 8, wherein MV0′ and MV1′ are derived based on MV1 incase that a collocated picture is in the reference list
 1. 11. Themethod of claim 1, the conversion generates the current block from thebitstream.
 12. The method of claim 1, wherein the conversion generatesthe bitstream from the current block.
 13. The method of claim 1, whereinperforming the conversion comprises parsing the bitstream based on oneor more decoding rules.
 14. A video processing apparatus comprising aprocessor and a non-transitory memory with instructions thereon, whereinthe instructions upon execution by the processor, cause the processorto: insert, for a conversion between a current block of a video and abitstream of the video that uses a sub-block merge candidate list, zeromotion non-affine padding candidates into the sub-block merge candidatelist in case that the sub-block merge candidate list is not fulfilled;and perform, subsequent to the inserting, the conversion.
 15. The videoprocessing apparatus of claim 14, wherein the instructions uponexecution by the processor, cause the processor to: set an affine usageflag of the current block to zero.
 16. The video processing apparatus ofclaim 14, wherein the inserting is further based on whether an affineusage flag in the bitstream is off.
 17. The video processing apparatusof claim 14, wherein the instructions upon execution by the processor,cause the processor to: determine whether a zero motion affine mergecandidate is inserted into the sub-block merge candidate list based onwhether affine prediction is enabled for the conversion of the currentblock.
 18. The video processing apparatus of claim 17, wherein the zeromotion affine merge candidate is not inserted into the sub-block mergecandidate list in case that an affine usage flag in the bitstream isoff.
 19. The video processing apparatus of claim 14, wherein theinstructions upon execution by the processor, cause the processor to:determine motion vectors using a rule that determines that the motionvectors are derived from one or more motion vectors of a block coveringa corresponding position in a collocated picture.
 20. A non-transitorycomputer-readable recording medium storing a bitstream of a video whichis generated by a method performed by a video processing apparatus,wherein the method comprises: inserting zero motion non-affine paddingcandidates into the sub-block merge candidate list in case that thesub-block merge candidate list is not fulfilled; and generating thebitstream based on the inserting.